MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0

1.3 What Is New in MySQL 8.0

This section summarizes what has been added to, deprecated in, and removed from MySQL 8.0. A companion section lists MySQL server options and variables that have been added, deprecated, or removed in MySQL 8.0; see Section 1.4, “Server and Status Variables and Options Added, Deprecated, or Removed in MySQL 8.0”.

Features Added in MySQL 8.0

The following features have been added to MySQL 8.0:

  • Data dictionary.  MySQL now incorporates a transactional data dictionary that stores information about database objects. In previous MySQL releases, dictionary data was stored in metadata files and nontransactional tables. For more information, see Chapter 16, MySQL Data Dictionary.

  • Atomic data definition statements (Atomic DDL).  An atomic DDL statement combines the data dictionary updates, storage engine operations, and binary log writes associated with a DDL operation into a single, atomic transaction. For more information, see Section 15.1.1, “Atomic Data Definition Statement Support”.

  • Upgrade procedure.  Previously, after installation of a new version of MySQL, the MySQL server automatically upgrades the data dictionary tables at the next startup, after which the DBA is expected to invoke mysql_upgrade manually to upgrade the system tables in the mysql schema, as well as objects in other schemas such as the sys schema and user schemas.

    As of MySQL 8.0.16, the server performs the tasks previously handled by mysql_upgrade. After installation of a new MySQL version, the server now automatically performs all necessary upgrade tasks at the next startup and is not dependent on the DBA invoking mysql_upgrade. In addition, the server updates the contents of the help tables (something mysql_upgrade did not do). A new --upgrade server option provides control over how the server performs automatic data dictionary and server upgrade operations. For more information, see Section 3.4, “What the MySQL Upgrade Process Upgrades”.

  • Session Reuse.  MySQL Server now supports SSL session reuse by default with a timeout setting to control how long the server maintains a session cache that establishes the period during which a client is permitted to request session reuse for new connections. All MySQL client programs support session reuse. For server-side and client-side configuration information, see Section 8.3.5, “Reusing SSL Sessions”.

    In addition, C applications now can use the C API capabilities to enable session reuse for encrypted connections (see SSL Session Reuse).

  • Security and account management.  These enhancements were added to improve security and enable greater DBA flexibility in account management:

    • MySQL Enterprise Audit now supports using the scheduler component to configure and execute a recurring task to flush the in-memory cache. For setup instructions, see Enabling the Audit Log Flush Task.

    • A new password-validation system variable permits the configuration and enforcement of a minimum number of characters that users must change when attempting to replace their own MySQL account passwords. This new verification setting is a percentage of the total characters in the current password. For example, if validate_password.changed_characters_percentage has a value of 50, at least half of the characters in the replacement account password must not be present in the current password, or the password is rejected. For more information, see Section 8.4.3, “The Password Validation Component”.

    • MySQL Enterprise Edition now provides data masking and de-identification capabilities based on components, rather than being based on a plugin library that was introduced in MySQL 8.0.13. MySQL Enterprise Data Masking and De-Identification components support for multibyte characters, masking dictionaries stored in a database table, and several new functions. For more information, see Section 8.5.1, “Data-Masking Components Versus the Data-Masking Plugin”.

    • Prior to MySQL 8.0.33, the mysql system database was used for MySQL Enterprise Audit's persistent storage of filter and user account data. For enhanced flexibility, the new audit_log_database server system variable now permits specifying other databases in the global schema namespace at server startup. The mysql system database is the default setting for table storage.

    • The grant tables in the mysql system database are now InnoDB (transactional) tables. Previously, these were MyISAM (nontransactional) tables. The change of grant table storage engine underlies an accompanying change to the behavior of account-management statements. Previously, an account-management statement (such as CREATE USER or DROP USER) that named multiple users could succeed for some users and fail for others. Now, each statement is transactional and either succeeds for all named users or rolls back and has no effect if any error occurs. The statement is written to the binary log if it succeeds, but not if it fails; in that case, rollback occurs and no changes are made. For more information, see Section 15.1.1, “Atomic Data Definition Statement Support”.

    • A new caching_sha2_password authentication plugin is available. Like the sha256_password plugin, caching_sha2_password implements SHA-256 password hashing, but uses caching to address latency issues at connect time. It also supports more transport protocols and does not require linking against OpenSSL for RSA key pair-based password-exchange capabilities. See Section, “Caching SHA-2 Pluggable Authentication”.

      The caching_sha2_password and sha256_password authentication plugins provide more secure password encryption than the mysql_native_password plugin (deprecated in 8.0.34), and caching_sha2_password provides better performance than sha256_password. Due to these superior security and performance characteristics of caching_sha2_password, it is now the preferred authentication plugin, and is also the default authentication plugin rather than mysql_native_password. For information about the implications of this change of default plugin for server operation and compatibility of the server with clients and connectors, see caching_sha2_password as the Preferred Authentication Plugin.

    • The MySQL Enterprise Edition SASL LDAP authentication plugin now supports GSSAPI/Kerberos as an authentication method for MySQL clients and servers on Linux. This is useful in Linux environments where applications access LDAP using Microsoft Active Directory, which has Kerberos enabled by default. See LDAP Authentication Methods.

    • MySQL Enterprise Edition now supports an authentication method that enables users to authenticate to MySQL Server using Kerberos, provided that appropriate Kerberos tickets are available or can be obtained. For details, see Section, “Kerberos Pluggable Authentication”.

    • MySQL now supports roles, which are named collections of privileges. Roles can be created and dropped. Roles can have privileges granted to and revoked from them. Roles can be granted to and revoked from user accounts. The active applicable roles for an account can be selected from among those granted to the account, and can be changed during sessions for that account. For more information, see Section 8.2.10, “Using Roles”.

    • MySQL now incorporates the concept of user account categories, with system and regular users distinguished according to whether they have the SYSTEM_USER privilege. See Section 8.2.11, “Account Categories”.

    • Previously, it was not possible to grant privileges that apply globally except for certain schemas. This is now possible if the partial_revokes system variable is enabled. See Section 8.2.12, “Privilege Restriction Using Partial Revokes”.

    • The GRANT statement has an AS user [WITH ROLE] clause that specifies additional information about the privilege context to use for statement execution. This syntax is visible at the SQL level, although its primary purpose is to enable uniform replication across all nodes of grantor privilege restrictions imposed by partial revokes, by causing those restrictions to appear in the binary log. See Section, “GRANT Statement”.

    • MySQL now maintains information about password history, enabling restrictions on reuse of previous passwords. DBAs can require that new passwords not be selected from previous passwords for some number of password changes or period of time. It is possible to establish password-reuse policy globally as well as on a per-account basis.

      It is now possible to require that attempts to change account passwords be verified by specifying the current password to be replaced. This enables DBAs to prevent users from changing password without proving that they know the current password. It is possible to establish password-verification policy globally as well as on a per-account basis.

      Accounts are now permitted to have dual passwords, which enables phased password changes to be performed seamlessly in complex multiple-server systems, without downtime.

      MySQL now enables administrators to configure user accounts such that too many consecutive login failures due to incorrect passwords cause temporary account locking. The required number of failures and the lock time are configurable per account.

      These new capabilities provide DBAs more complete control over password management. For more information, see Section 8.2.15, “Password Management”.

    • MySQL now supports FIPS mode, if compiled using OpenSSL, and an OpenSSL library and FIPS Object Module are available at runtime. FIPS mode imposes conditions on cryptographic operations such as restrictions on acceptable encryption algorithms or requirements for longer key lengths. See Section 8.8, “FIPS Support”.

    • The TLS context the server uses for new connections now is reconfigurable at runtime. This capability may be useful, for example, to avoid restarting a MySQL server that has been running so long that its SSL certificate has expired. See Server-Side Runtime Configuration and Monitoring for Encrypted Connections.

    • OpenSSL 1.1.1 supports the TLS v1.3 protocol for encrypted connections, and MySQL 8.0.16 and higher supports TLS v1.3 as well, if both the server and client are compiled using OpenSSL 1.1.1 or higher. See Section 8.3.2, “Encrypted Connection TLS Protocols and Ciphers”.

    • MySQL now sets the access control granted to clients on the named pipe to the minimum necessary for successful communication on Windows. Newer MySQL client software can open named pipe connections without any additional configuration. If older client software cannot be upgraded immediately, the new named_pipe_full_access_group system variable can be used to give a Windows group the necessary permissions to open a named pipe connection. Membership in the full-access group should be restricted and temporary.

    • Previously, MySQL user accounts authenticated to the server using a single authentication method. As of MySQL 8.0.27, MySQL supports multifactor authentication (MFA), which makes it possible to create accounts that have up to three authentication methods. MFA support entails these changes:

      • CREATE USER and ALTER USER syntax has been extended to permit specification of multiple authentication methods.

      • The authentication_policy system variable enables MFA policy to be established by controlling how many factors can be used and the types of authentication permitted for each factor. This places constraints on how the authentication-related clauses of CREATE USER and ALTER USER statements may be used.

      • Client programs have new --password1, --password2, and --password3 command-line options for specifying multiple passwords. For applications that use the C API, the new MYSQL_OPT_USER_PASSWORD option for the mysql_options4() C API function enables the same capability.

      In addition, MySQL Enterprise Edition now supports authentication to MySQL Server using devices such as smart cards, security keys, and biometric readers. This authentication method is based on the Fast Identity Online (FIDO) standard, and uses a pair of plugins, authentication_fido on the server side and authentication_fido_client on the client side. The server-side FIDO authentication plugin is included only in MySQL Enterprise Edition distributions. It is not included in MySQL community distributions. However, the client-side plugin is included in all distributions, including community distributions. This enables clients from any distribution to connect to a server that has the server-side plugin loaded.

      Multifactor authentication can use existing MySQL authentication methods, the new FIDO authentication method, or a combination of both. For more information, see Section 8.2.18, “Multifactor Authentication”, and Section, “FIDO Pluggable Authentication”.

  • Resource management.  MySQL now supports creation and management of resource groups, and permits assigning threads running within the server to particular groups so that threads execute according to the resources available to the group. Group attributes enable control over its resources, to enable or restrict resource consumption by threads in the group. DBAs can modify these attributes as appropriate for different workloads. Currently, CPU time is a manageable resource, represented by the concept of virtual CPU as a term that includes CPU cores, hyperthreads, hardware threads, and so forth. The server determines at startup how many virtual CPUs are available, and database administrators with appropriate privileges can associate these CPUs with resource groups and assign threads to groups. For more information, see Section 7.1.16, “Resource Groups”.

  • Table encryption management.  Table encryption can now be managed globally by defining and enforcing encryption defaults. The default_table_encryption variable defines an encryption default for newly created schemas and general tablespace. The encryption default for a schema can also be defined using the DEFAULT ENCRYPTION clause when creating a schema. By default, a table inherits the encryption of the schema or general tablespace it is created in. Encryption defaults are enforced by enabling the table_encryption_privilege_check variable. The privilege check occurs when creating or altering a schema or general tablespace with an encryption setting that differs from the default_table_encryption setting, or when creating or altering a table with an encryption setting that differs from the default schema encryption. The TABLE_ENCRYPTION_ADMIN privilege permits overriding default encryption settings when table_encryption_privilege_check is enabled. For more information, see Defining an Encryption Default for Schemas and General Tablespaces.

  • InnoDB enhancements.  These InnoDB enhancements were added:

    • The current maximum auto-increment counter value is written to the redo log each time the value changes, and saved to an engine-private system table on each checkpoint. These changes make the current maximum auto-increment counter value persistent across server restarts. Additionally:

      • A server restart no longer cancels the effect of the AUTO_INCREMENT = N table option. If you initialize the auto-increment counter to a specific value, or if you alter the auto-increment counter value to a larger value, the new value is persisted across server restarts.

      • A server restart immediately following a ROLLBACK operation no longer results in the reuse of auto-increment values that were allocated to the rolled-back transaction.

      • If you modify an AUTO_INCREMENT column value to a value larger than the current maximum auto-increment value (in an UPDATE operation, for example), the new value is persisted, and subsequent INSERT operations allocate auto-increment values starting from the new, larger value.

      For more information, see Section, “AUTO_INCREMENT Handling in InnoDB”, and InnoDB AUTO_INCREMENT Counter Initialization.

    • When encountering index tree corruption, InnoDB writes a corruption flag to the redo log, which makes the corruption flag crash safe. InnoDB also writes in-memory corruption flag data to an engine-private system table on each checkpoint. During recovery, InnoDB reads corruption flags from both locations and merges results before marking in-memory table and index objects as corrupt.

    • The InnoDB memcached plugin supports multiple get operations (fetching multiple key-value pairs in a single memcached query) and range queries. See Section 17.20.4, “InnoDB memcached Multiple get and Range Query Support”.

    • A new dynamic variable, innodb_deadlock_detect, may be used to disable deadlock detection. On high concurrency systems, deadlock detection can cause a slowdown when numerous threads wait for the same lock. At times, it may be more efficient to disable deadlock detection and rely on the innodb_lock_wait_timeout setting for transaction rollback when a deadlock occurs.

    • The new Information Schema INNODB_CACHED_INDEXES table reports the number of index pages cached in the InnoDB buffer pool for each index.

    • InnoDB temporary tables are now created in the shared temporary tablespace, ibtmp1.

    • The InnoDB tablespace encryption feature supports encryption of redo log and undo log data. See Redo Log Encryption, and Undo Log Encryption.

    • InnoDB supports NOWAIT and SKIP LOCKED options with SELECT ... FOR SHARE and SELECT ... FOR UPDATE locking read statements. NOWAIT causes the statement to return immediately if a requested row is locked by another transaction. SKIP LOCKED removes locked rows from the result set. See Locking Read Concurrency with NOWAIT and SKIP LOCKED.

      SELECT ... FOR SHARE replaces SELECT ... LOCK IN SHARE MODE, but LOCK IN SHARE MODE remains available for backward compatibility. The statements are equivalent. However, FOR UPDATE and FOR SHARE support NOWAIT, SKIP LOCKED, and OF tbl_name options. See Section 15.2.13, “SELECT Statement”.

      OF tbl_name applies locking queries to named tables.

    • ADD PARTITION, DROP PARTITION, COALESCE PARTITION, REORGANIZE PARTITION, and REBUILD PARTITION ALTER TABLE options are supported by native partitioning in-place APIs and may be used with ALGORITHM={COPY|INPLACE} and LOCK clauses.

      DROP PARTITION with ALGORITHM=INPLACE deletes data stored in the partition and drops the partition. However, DROP PARTITION with ALGORITHM=COPY or old_alter_table=ON rebuilds the partitioned table and attempts to move data from the dropped partition to another partition with a compatible PARTITION ... VALUES definition. Data that cannot be moved to another partition is deleted.

    • The InnoDB storage engine now uses the MySQL data dictionary rather than its own storage engine-specific data dictionary. For information about the data dictionary, see Chapter 16, MySQL Data Dictionary.

    • mysql system tables and data dictionary tables are now created in a single InnoDB tablespace file named mysql.ibd in the MySQL data directory. Previously, these tables were created in individual InnoDB tablespace files in the mysql database directory.

    • The following undo tablespace changes are introduced in MySQL 8.0:

      • By default, undo logs now reside in two undo tablespaces that are created when the MySQL instance is initialized. Undo logs are no longer created in the system tablespace.

      • As of MySQL 8.0.14, additional undo tablespaces can be created in a chosen location at runtime using CREATE UNDO TABLESPACE syntax.

        CREATE UNDO TABLESPACE tablespace_name ADD DATAFILE 'file_name.ibu';

        Undo tablespaces created using CREATE UNDO TABLESPACE syntax can be dropped at runtime using DROP UNDO TABLESPACE syntax.

        DROP UNDO TABLESPACE tablespace_name;

        ALTER UNDO TABLESPACE syntax can be used to mark an undo tablespace as active or inactive.


        A STATE column that shows the state of a tablespace was added to the Information Schema INNODB_TABLESPACES table. An undo tablespace must be in an empty state before it can be dropped.

      • The innodb_undo_log_truncate variable is enabled by default.

      • The innodb_rollback_segments variable defines the number of rollback segments per undo tablespace. Previously, innodb_rollback_segments specified the total number of rollback segments for the MySQL instance. This change increases the number of rollback segments available for concurrent transactions. More rollback segments increases the likelihood that concurrent transactions use separate rollback segments for undo logs, resulting in less resource contention.

    • Default values for variables that affect buffer pool preflushing and flushing behavior were modified:

      • The innodb_max_dirty_pages_pct_lwm default value is now 10. The previous default value of 0 disables buffer pool preflushing. A value of 10 enables preflushing when the percentage of dirty pages in the buffer pool exceeds 10%. Enabling preflushing improves performance consistency.

      • The innodb_max_dirty_pages_pct default value was increased from 75 to 90. InnoDB attempts to flush data from the buffer pool so that the percentage of dirty pages does not exceed this value. The increased default value permits a greater percentage of dirty pages in the buffer pool.

    • The default innodb_autoinc_lock_mode setting is now 2 (interleaved). Interleaved lock mode permits the execution of multi-row inserts in parallel, which improves concurrency and scalability. The new innodb_autoinc_lock_mode default setting reflects the change from statement-based replication to row based replication as the default replication type in MySQL 5.7. Statement-based replication requires the consecutive auto-increment lock mode (the previous default) to ensure that auto-increment values are assigned in a predictable and repeatable order for a given sequence of SQL statements, whereas row-based replication is not sensitive to the execution order of SQL statements. For more information, see InnoDB AUTO_INCREMENT Lock Modes.

      For systems that use statement-based replication, the new innodb_autoinc_lock_mode default setting may break applications that depend on sequential auto-increment values. To restore the previous default, set innodb_autoinc_lock_mode to 1.

    • Renaming a general tablespace is supported by ALTER TABLESPACE ... RENAME TO syntax.

    • The new innodb_dedicated_server variable, which is disabled by default, can be used to have InnoDB automatically configure the following options according to the amount of memory detected on the server:

      This option is intended for MySQL server instances that run on a dedicated server. For more information, see Section 17.8.12, “Enabling Automatic Configuration for a Dedicated MySQL Server”.

    • The new Information Schema INNODB_TABLESPACES_BRIEF view provides space, name, path, flag, and space type data for InnoDB tablespaces.

    • The zlib library version bundled with MySQL was raised from version 1.2.3 to version 1.2.11. MySQL implements compression with the help of the zlib library.

      If you use InnoDB compressed tables, see Section 3.5, “Changes in MySQL 8.0” for related upgrade implications.

    • Serialized dictionary information (SDI) is present in all InnoDB tablespace files except for global temporary tablespace and undo tablespace files. SDI is serialized metadata for table and tablespace objects. The presence of SDI data provides metadata redundancy. For example, dictionary object metadata may be extracted from tablespace files if the data dictionary becomes unavailable. SDI extraction is performed using the ibd2sdi tool. SDI data is stored in JSON format.

      The inclusion of SDI data in tablespace files increases tablespace file size. An SDI record requires a single index page, which is 16KB in size by default. However, SDI data is compressed when it is stored to reduce the storage footprint.

    • The InnoDB storage engine now supports atomic DDL, which ensures that DDL operations are either fully committed or rolled back, even if the server halts during the operation. For more information, see Section 15.1.1, “Atomic Data Definition Statement Support”.

    • Tablespace files can be moved or restored to a new location while the server is offline using the innodb_directories option. For more information, see Section, “Moving Tablespace Files While the Server is Offline”.

    • The following redo logging optimizations were implemented:

      • User threads can now write concurrently to the log buffer without synchronizing writes.

      • User threads can now add dirty pages to the flush list in a relaxed order.

      • A dedicated log thread is now responsible for writing the log buffer to the system buffers, flushing system buffers to disk, notifying user threads about written and flushed redo, maintaining the lag required for the relaxed flush list order, and write checkpoints.

      • System variables were added for configuring the use of spin delay by user threads waiting for flushed redo:

      • The innodb_log_buffer_size variable is now dynamic, which permits resizing of the log buffer while the server is running.

      For more information, see Section 10.5.4, “Optimizing InnoDB Redo Logging”.

    • As of MySQL 8.0.12, undo logging is supported for small updates to large object (LOB) data, which improves performance of LOB updates that are 100 bytes in size or less. Previously, LOB updates were a minimum of one LOB page in size, which is less than optimal for updates that might only modify a few bytes. This enhancement builds upon support added in MySQL 8.0.4 for partial update of LOB data.

    • As of MySQL 8.0.12, ALGORITHM=INSTANT is supported for the following ALTER TABLE operations:

      • Adding a column. This feature is also referred to as Instant ADD COLUMN. Limitations apply. See Section 17.12.1, “Online DDL Operations”.

      • Adding or dropping a virtual column.

      • Adding or dropping a column default value.

      • Modifying the definition of an ENUM or SET column.

      • Changing the index type.

      • Renaming a table.

      Operations that support ALGORITHM=INSTANT only modify metadata in the data dictionary. No metadata locks are taken on the table, and table data is unaffected, making the operations instantaneous. If not specified explicitly, ALGORITHM=INSTANT is used by default by operations that support it. If ALGORITHM=INSTANT is specified but not supported, the operation fails immediately with an error.

      For more information about operations that support ALGORITHM=INSTANT, see Section 17.12.1, “Online DDL Operations”.

    • As of MySQL 8.0.13, the TempTable storage engine supports storage of binary large object (BLOB) type columns. This enhancement improves performance for queries that use temporary tables containing BLOB data. Previously, temporary tables that contained BLOB data were stored in the on-disk storage engine defined by internal_tmp_disk_storage_engine. For more information, see Section 10.4.4, “Internal Temporary Table Use in MySQL”.

    • As of MySQL 8.0.13, the InnoDB data-at-rest encryption feature supports general tablespaces. Previously, only file-per-table tablespaces could be encrypted. To support encryption of general tablespaces, CREATE TABLESPACE and ALTER TABLESPACE syntax was extended to include an ENCRYPTION clause.

      The Information Schema INNODB_TABLESPACES table now includes an ENCRYPTION column that indicates whether or not a tablespace is encrypted.

      The stage/innodb/alter tablespace (encryption) Performance Schema stage instrument was added to permit monitoring of general tablespace encryption operations.

    • Disabling the innodb_buffer_pool_in_core_file variable reduces the size of core files by excluding InnoDB buffer pool pages. To use this variable, the core_file variable must be enabled and the operating system must support the MADV_DONTDUMP non-POSIX extension to madvise(), which is supported in Linux 3.4 and later. For more information, see Section, “Excluding Buffer Pool Pages from Core Files”.

    • As of MySQL 8.0.13, user-created temporary tables and internal temporary tables created by the optimizer are stored in session temporary tablespaces that are allocated to a session from a pool of temporary tablespaces. When a session disconnects, its temporary tablespaces are truncated and released back to the pool. In previous releases, temporary tables were created in the global temporary tablespace (ibtmp1), which did not return disk space to the operating system after temporary tables were dropped.

      The innodb_temp_tablespaces_dir variable defines the location where session temporary tablespaces are created. The default location is the #innodb_temp directory in the data directory.

      The INNODB_SESSION_TEMP_TABLESPACES table provides metadata about session temporary tablespaces.

      The global temporary tablespace (ibtmp1) now stores rollback segments for changes made to user-created temporary tables.

    • As of MySQL 8.0.14, InnoDB supports parallel clustered index reads, which can improve CHECK TABLE performance. This feature does not apply to secondary index scans. The innodb_parallel_read_threads session variable must be set to a value greater than 1 for parallel clustered index reads to occur. The default value is 4. The actual number of threads used to perform a parallel clustered index read is determined by the innodb_parallel_read_threads setting or the number of index subtrees to scan, whichever is smaller.

    • As of 8.0.14, when the innodb_dedicated_server variable is enabled, the size and number of log files are configured according to the automatically configured buffer pool size. Previously, log file size was configured according to the amount of memory detected on the server, and the number of log files was not configured automatically.

    • As of 8.0.14, the ADD DATAFILE clause of the CREATE TABLESPACE statement is optional, which permits users without the FILE privilege to create tablespaces. A CREATE TABLESPACE statement executed without an ADD DATAFILE clause implicitly creates a tablespace data file with a unique file name.

    • By default, when the amount of memory occupied by the TempTable storage engine exceeds the memory limit defined by the temptable_max_ram variable, the TempTable storage engine begins allocating memory-mapped temporary files from disk. As of MySQL 8.0.16, this behavior is controlled by the temptable_use_mmap variable. Disabling temptable_use_mmap causes the TempTable storage engine to use InnoDB on-disk internal temporary tables instead of memory-mapped files as its overflow mechanism. For more information, see Internal Temporary Table Storage Engine.

    • As of MySQL 8.0.16, the InnoDB data-at-rest encryption feature supports encryption of the mysql system tablespace. The mysql system tablespace contains the mysql system database and the MySQL data dictionary tables. For more information, see Section 17.13, “InnoDB Data-at-Rest Encryption”.

    • The innodb_spin_wait_pause_multiplier variable, introduced in MySQL 8.0.16, provides greater control over the duration of spin-lock polling delays that occur when a thread waits to acquire a mutex or rw-lock. Delays can be tuned more finely to account for differences in PAUSE instruction duration on different processor architectures. For more information, see Section 17.8.8, “Configuring Spin Lock Polling”.

    • InnoDB parallel read thread performance for large data sets was improved in MySQL 8.0.17 through better utilization of read threads, through a reduction in read thread I/O for prefetch activity that occurs during parallel scans, and through support for parallel scanning of partitions.

      The parallel read thread feature is controlled by the innodb_parallel_read_threads variable. The maximum setting is now 256, which is the total number of threads for all client connections. If the thread limit is reached, connections fall back to using a single thread.

    • The innodb_idle_flush_pct variable, introduced in MySQL 8.0.18, permits placing a limit on page flushing during idle periods, which can help extend the life of solid state storage devices. See Limiting Buffer Flushing During Idle Periods.

    • Efficient sampling of InnoDB data for the purpose of generating histogram statistics is supported as of MySQL 8.0.19. See Histogram Statistics Analysis.

    • As of MySQL 8.0.20, the doublewrite buffer storage area resides in doublewrite files. In previous releases, the storage area resided in the system tablespace. Moving the storage area out of the system tablespace reduces write latency, increases throughput, and provides flexibility with respect to placement of doublewrite buffer pages. The following system variables were introduced for advanced doublewrite buffer configuration:

      For more information, see Section 17.6.4, “Doublewrite Buffer”.

    • The Contention-Aware Transaction Scheduling (CATS) algorithm, which prioritizes transactions that are waiting for locks, was improved in MySQL 8.0.20. Transaction scheduling weight computation is now performed a separate thread entirely, which improves computation performance and accuracy.

      The First In First Out (FIFO) algorithm, which had also been used for transaction scheduling, was removed. The FIFO algorithm was rendered redundant by CATS algorithm enhancements. Transaction scheduling previously performed by the FIFO algorithm is now performed by the CATS algorithm.

      A TRX_SCHEDULE_WEIGHT column was added to the INFORMATION_SCHEMA.INNODB_TRX table, which permits querying transaction scheduling weights assigned by the CATS algorithm.

      The following INNODB_METRICS counters were added for monitoring code-level transaction scheduling events:

      • lock_rec_release_attempts

        The number of attempts to release record locks.

      • lock_rec_grant_attempts

        The number of attempts to grant record locks.

      • lock_schedule_refreshes

        The number of times the wait-for graph was analyzed to update transaction schedule weights.

      For more information, see Section 17.7.6, “Transaction Scheduling”.

    • As of MySQL 8.0.21, to improve concurrency for operations that require access to lock queues for table and row resources, the lock system mutex (lock_sys->mutex) was replaced in by sharded latches, and lock queues were grouped into table and page lock queue shards, with each shard protected by a dedicated mutex. Previously, the single lock system mutex protected all lock queues, which was a point of contention on high-concurrency systems. The new sharded implementation permits more granular access to lock queues.

      The lock system mutex (lock_sys->mutex) was replaced by the following sharded latches:

      • A global latch (lock_sys->latches.global_latch) consisting of 64 read-write lock objects (rw_lock_t). Access to an individual lock queue requires a shared global latch and a latch on the lock queue shard. Operations that require access to all lock queues take an exclusive global latch, which latches all table and page lock queue shards.

      • Table shard latches (lock_sys->latches.table_shards.mutexes), implemented as an array of 512 mutexes, with each mutex dedicated to one of 512 table lock queue shards.

      • Page shard latches (lock_sys->latches.page_shards.mutexes), implemented as an array of 512 mutexes, with each mutex dedicated to one of 512 page lock queue shards.

      The Performance Schema wait/synch/mutex/innodb/lock_mutex instrument for monitoring the single lock system mutex was replaced by instruments for monitoring the new global, table shard, and page shard latches:

      • wait/synch/sxlock/innodb/lock_sys_global_rw_lock

      • wait/synch/mutex/innodb/lock_sys_table_mutex

      • wait/synch/mutex/innodb/lock_sys_page_mutex

    • As of MySQL 8.0.21, table and table partition data files created outside of the data directory using the DATA DIRECTORY clause are restricted to directories known to InnoDB. This change permits database administrators to control where tablespace data files are created and ensures that the data files can be found during recovery.

      General and file-per-table tablespaces data files (.ibd files) can no longer be created in the undo tablespace directory (innodb_undo_directory) unless that directly is known to InnoDB.

      Known directories are those defined by the datadir, innodb_data_home_dir, and innodb_directories variables.

      Truncating an InnoDB table that resides in a file-per-table tablespace drops the existing tablespace and creates a new one. As of MySQL 8.0.21, InnoDB creates the new tablespace in the default location and writes a warning to the error log if the current tablespace directory is unknown. To have TRUNCATE TABLE create the tablespace in its current location, add the directory to the innodb_directories setting before running TRUNCATE TABLE.

    • As of MySQL 8.0.21, redo logging can be enabled and disabled using ALTER INSTANCE {ENABLE|DISABLE} INNODB REDO_LOG syntax. This functionality is intended for loading data into a new MySQL instance. Disabling redo logging helps speed up data loading by avoiding redo log writes.

      The new INNODB_REDO_LOG_ENABLE privilege permits enabling and disabling redo logging.

      The new Innodb_redo_log_enabled status variable permits monitoring redo logging status.

      See Disabling Redo Logging.

    • At startup, InnoDB validates the paths of known tablespace files against tablespace file paths stored in the data dictionary in case tablespace files have been moved to a different location. The new innodb_validate_tablespace_paths variable, introduced in MySQL 8.0.21, permits disabling tablespace path validation. This feature is intended for environments where tablespaces files are not moved. Disabling tablespace path validation improves startup time on systems with a large number of tablespace files.

      For more information, see Section, “Disabling Tablespace Path Validation”.

    • As of MySQL 8.0.21, on storage engines that support atomic DDL, the CREATE TABLE ... SELECT statement is logged as one transaction in the binary log when row-based replication is in use. Previously, it was logged as two transactions, one to create the table, and the other to insert data. With this change, CREATE TABLE ... SELECT statements are now safe for row-based replication and permitted for use with GTID-based replication. For more information, see Section 15.1.1, “Atomic Data Definition Statement Support”.

    • Truncating an undo tablespace on a busy system could affect performance due to associated flushing operations that remove old undo tablespace pages from the buffer pool and flush the initial pages of the new undo tablespace to disk. To address this issue, the flushing operations are removed as of MySQL 8.0.21.

      Old undo tablespace pages are released passively as they become least recently used, or are removed at the next full checkpoint. The initial pages of the new undo tablespace are now redo logged instead of flushed to disk during the truncate operation, which also improves durability of the undo tablespace truncate operation.

      To prevent potential issues caused by an excessive number of undo tablespace truncate operations, truncate operations on the same undo tablespace between checkpoints are now limited to 64. If the limit is exceeded, an undo tablespace can still be made inactive, but it is not truncated until after the next checkpoint.

      INNODB_METRICS counters associated with defunct undo truncate flushing operations were removed. Removed counters include: undo_truncate_sweep_count, undo_truncate_sweep_usec, undo_truncate_flush_count, and undo_truncate_flush_usec.

      See Section, “Undo Tablespaces”.

    • As of MySQL 8.0.22, the new innodb_extend_and_initialize variable permits configuring how InnoDB allocates space to file-per-table and general tablespaces on Linux. By default, when an operation requires additional space in a tablespace, InnoDB allocates pages to the tablespace and physically writes NULLs to those pages. This behavior affects performance if new pages are allocated frequently. You can disable innodb_extend_and_initialize on Linux systems to avoid physically writing NULLs to newly allocated tablespace pages. When innodb_extend_and_initialize is disabled, space is allocated using posix_fallocate() calls, which reserve space without physically writing NULLs.

      A posix_fallocate() operation is not atomic, which makes it possible for a failure to occur between allocating space to a tablespace file and updating the file metadata. Such a failure can leave newly allocated pages in an uninitialized state, resulting in a failure when InnoDB attempts to access those pages. To prevent this scenario, InnoDB writes a redo log record before allocating a new tablespace page. If a page allocation operation is interrupted, the operation is replayed from the redo log record during recovery.

    • As of MySQL 8.0.23, InnoDB supports encryption of doublewrite file pages belonging to encrypted tablespaces. The pages are encrypted using the encryption key of the associated tablespace. For more information, see Section 17.13, “InnoDB Data-at-Rest Encryption”.

    • The temptable_max_mmap variable, introduced in MySQL 8.0.23, defines the maximum amount of memory the TempTable storage engine is permitted to allocate from memory-mapped (MMAP) files before it starts storing internal temporary table data on disk. A setting of 0 disables allocation from MMAP files. For more information, see Section 10.4.4, “Internal Temporary Table Use in MySQL”.

    • The AUTOEXTEND_SIZE option, introduced in MySQL 8.0.23, defines the amount by which InnoDB extends the size of a tablespace when it becomes full, making it possible to extend tablespace size in larger increments. The AUTOEXTEND_SIZE option is supported with the CREATE TABLE, ALTER TABLE, CREATE TABLESPACE, and ALTER TABLESPACE statements. For more information, see Section, “Tablespace AUTOEXTEND_SIZE Configuration”.

      An AUTOEXTEND_SIZE size column was added to the Information Schema INNODB_TABLESPACES table.

    • The innodb_segment_reserve_factor system variable, introduced in MySQL 8.0.26, permits configuring the percentage of tablespace file segment pages that are reserved as empty pages. For more information, see Configuring the Percentage of Reserved File Segment Pages.

    • On platforms that support fdatasync() system calls, the innodb_use_fdatasync variable, introduced in MySQL 8.0.26, permits using fdatasync() instead of fsync() for operating system flushes. An fdatasync() system call does not flush changes to file metadata unless required for subsequent data retrieval, providing a potential performance benefit.

    • As of MySQL 8.0.28, the tmp_table_size variable defines the maximum size of any individual in-memory internal temporary table created by the TempTable storage engine. An appropriate size limit prevents individual queries from consuming an inordinate amount global TempTable resources. See Internal Temporary Table Storage Engine.

    • From MySQL 8.0.28, the innodb_open_files variable, which defines the number of files InnoDB can have open at one time, can be set at runtime using a SELECT innodb_set_open_files_limit(N) statement. The statement executes a stored procedure that sets the new limit.

      To prevent non-LRU manged files from consuming the entire innodb_open_files limit, non-LRU managed files are limited to 90 percent of the innodb_open_files limit, which reserves 10 percent of the innodb_open_files limit for LRU managed files.

      The innodb_open_files limit includes temporary tablespace files, which were not counted toward the limit previously.

    • From MySQL 8.0.28, InnoDB supports ALTER TABLE ... RENAME COLUMN operations using ALGORITHM=INSTANT.

      For more information about this and other DDL operations that support ALGORITHM=INSTANT, see Section 17.12.1, “Online DDL Operations”.

    • From MySQL 8.0.29, InnoDB supports ALTER TABLE ... DROP COLUMN operations using ALGORITHM=INSTANT.

      Prior to MySQL 8.0.29, an instantly added column could only be added as the last column of the table. From MySQL 8.0.29, an instantly added column can be added to any position in the table.

      Instantly added or dropped columns create a new version of the affected row. Up to 64 row versions are permitted. A new TOTAL_ROW_VERSIONS column was added to the Information Schema INNODB_TABLES table to track the number of row versions.

      For more information about DDL operations that support ALGORITHM=INSTANT, see Section 17.12.1, “Online DDL Operations”.

    • From MySQL 8.0.30, the innodb_doublewrite system variable supports DETECT_ONLY and DETECT_AND_RECOVER settings. With the DETECT_ONLY setting, database page content is not written to the doublewrite buffer, and recovery does not use the doublewrite buffer to fix incomplete page writes. This lightweight setting is intended for detecting incomplete page writes only. The DETECT_AND_RECOVER setting is equivalent to the existing ON setting. For more information, see Section 17.6.4, “Doublewrite Buffer”.

    • From MySQL 8.0.30, InnoDB supports dynamic configuration of redo log capacity. The innodb_redo_log_capacity system variable can be set at runtime to increase or decrease the total amount of disk space occupied by redo log files.

      With this change, the number of redo log files and their default location has also changed. From MySQL 8.0.30, InnoDB maintains 32 redo log files in the #innodb_redo directory in the data directory. Previously, InnoDB created two redo log files in the data directory by default, and the number and size of redo log files were controlled by the innodb_log_files_in_group and innodb_log_file_size variables. These two variables are now deprecated.

      When the innodb_redo_log_capacity setting is defined, innodb_log_files_in_group and innodb_log_file_size settings are ignored; otherwise, those settings are used to compute the innodb_redo_log_capacity setting (innodb_log_files_in_group * innodb_log_file_size = innodb_redo_log_capacity). If none of those variables are set, redo log capacity is set to the innodb_redo_log_capacity default value, which is 104857600 bytes (100MB).

      Several status variables are provided for monitoring the redo log and redo log resizing operations.

      For more information, see Section 17.6.5, “Redo Log”.

    • With MySQL 8.0.31, there are two new status variables for monitoring online buffer pool resizing operations. The Innodb_buffer_pool_resize_status_code status variable reports a status code indicating the stage of an online buffer pool resizing operation. The Innodb_buffer_pool_resize_status_progress status variable reports a percentage value indicating the progress of each stage.

      For more information, see Section, “Configuring InnoDB Buffer Pool Size”.

  • Character set support.  The default character set has changed from latin1 to utf8mb4. The utf8mb4 character set has several new collations, including utf8mb4_ja_0900_as_cs, the first Japanese language-specific collation available for Unicode in MySQL. For more information, see Section 12.10.1, “Unicode Character Sets”.

  • JSON enhancements.  The following enhancements or additions were made to MySQL's JSON functionality:

    • Added the ->> (inline path) operator, which is equivalent to calling JSON_UNQUOTE() on the result of JSON_EXTRACT().

      This is a refinement of the column path operator -> introduced in MySQL 5.7; col->>"$.path" is equivalent to JSON_UNQUOTE(col->"$.path"). The inline path operator can be used wherever you can use JSON_UNQUOTE(JSON_EXTRACT()), such SELECT column lists, WHERE and HAVING clauses, and ORDER BY and GROUP BY clauses. For more information, see the description of the operator, as well as JSON Path Syntax.

    • Added two JSON aggregation functions JSON_ARRAYAGG() and JSON_OBJECTAGG(). JSON_ARRAYAGG() takes a column or expression as its argument, and aggregates the result as a single JSON array. The expression can evaluate to any MySQL data type; this does not have to be a JSON value. JSON_OBJECTAGG() takes two columns or expressions which it interprets as a key and a value; it returns the result as a single JSON object. For more information and examples, see Section 14.19, “Aggregate Functions”.

    • Added the JSON utility function JSON_PRETTY(), which outputs an existing JSON value in an easy-to-read format; each JSON object member or array value is printed on a separate line, and a child object or array is intended 2 spaces with respect to its parent.

      This function also works with a string that can be parsed as a JSON value.

      For more detailed information and examples, see Section 14.17.8, “JSON Utility Functions”.

    • When sorting JSON values in a query using ORDER BY, each value is now represented by a variable-length part of the sort key, rather than a part of a fixed 1K in size. In many cases this can reduce excessive usage. For example, a scalar INT or even BIGINT value actually requires very few bytes, so that the remainder of this space (up to 90% or more) was taken up by padding. This change has the following benefits for performance:

      • Sort buffer space is now used more effectively, so that filesorts need not flush to disk as early or often as with fixed-length sort keys. This means that more data can be sorted in memory, avoiding unnecessary disk access.

      • Shorter keys can be compared more quickly than longer ones, providing a noticeable improvement in performance. This is true for sorts performed entirely in memory as well as for sorts that require writing to and reading from disk.

    • Added support in MySQL 8.0.2 for partial, in-place updates of JSON column values, which is more efficient than completely removing an existing JSON value and writing a new one in its place, as was done previously when updating any JSON column. For this optimization to be applied, the update must be applied using JSON_SET(), JSON_REPLACE(), or JSON_REMOVE(). New elements cannot be added to the JSON document being updated; values within the document cannot take more space than they did before the update. See Partial Updates of JSON Values, for a detailed discussion of the requirements.

      Partial updates of JSON documents can be written to the binary log, taking up less space than logging complete JSON documents. Partial updates are always logged as such when statement-based replication is in use. For this to work with row-based replication, you must first set binlog_row_value_options=PARTIAL_JSON; see this variable's description for more information.

    • Added the JSON utility functions JSON_STORAGE_SIZE() and JSON_STORAGE_FREE(). JSON_STORAGE_SIZE() returns the storage space in bytes used for the binary representation of a JSON document prior to any partial update (see previous item). JSON_STORAGE_FREE() shows the amount of space remaining in a table column of type JSON after it has been partially updated using JSON_SET() or JSON_REPLACE(); this is greater than zero if the binary representation of the new value is less than that of the previous value.

      Each of these functions also accepts a valid string representation of a JSON document. For such a value, JSON_STORAGE_SIZE() returns the space used by its binary representation following its conversion to a JSON document. For a variable containing the string representation of a JSON document, JSON_STORAGE_FREE() returns zero. Either function produces an error if its (non-null) argument cannot be parsed as a valid JSON document, and NULL if the argument is NULL.

      For more information and examples, see Section 14.17.8, “JSON Utility Functions”.

      JSON_STORAGE_SIZE() and JSON_STORAGE_FREE() were implemented in MySQL 8.0.2.

    • Added support in MySQL 8.0.2 for ranges such as $[1 to 5] in XPath expressions. Also added support in this version for the last keyword and relative addressing, such that $[last] always selects the last (highest-numbered) element in the array and $[last-1] the next to last element. last and expressions using it can also be included in range definitions. For example, $[last-2 to last-1] returns the last two elements but one from an array. See Searching and Modifying JSON Values, for additional information and examples.

    • Added a JSON merge function intended to conform to RFC 7396. JSON_MERGE_PATCH(), when used on 2 JSON objects, merges them into a single JSON object that has as members a union of the following sets:

      • Each member of the first object for which there is no member with the same key in the second object.

      • Each member of the second object for which there is no member having the same key in the first object, and whose value is not the JSON null literal.

      • Each member having a key that exists in both objects, and whose value in the second object is not the JSON null literal.

      As part of this work, the JSON_MERGE() function has been renamed JSON_MERGE_PRESERVE(). JSON_MERGE() continues to be recognized as an alias for JSON_MERGE_PRESERVE() in MySQL 8.0, but is now deprecated and is subject to removal in a future version of MySQL.

      For more information and examples, see Section 14.17.4, “Functions That Modify JSON Values”.

    • Implemented last duplicate key wins normalization of duplicate keys, consistent with RFC 7159 and most JavaScript parsers. An example of this behavior is shown here, where only the rightmost member having the key x is preserved:

      mysql> SELECT JSON_OBJECT('x', '32', 'y', '[true, false]',
           >                     'x', '"abc"', 'x', '100') AS Result;
      | Result                             |
      | {"x": "100", "y": "[true, false]"} |
      1 row in set (0.00 sec)

      Values inserted into MySQL JSON columns are also normalized in this way, as shown in this example:

      mysql> CREATE TABLE t1 (c1 JSON);
      mysql> INSERT INTO t1 VALUES ('{"x": 17, "x": "red", "x": [3, 5, 7]}');
      mysql> SELECT c1 FROM t1;
      | c1               |
      | {"x": [3, 5, 7]} |

      This is an incompatible change from previous versions of MySQL, where a first duplicate key wins algorithm was used in such cases.

      See Normalization, Merging, and Autowrapping of JSON Values, for more information and examples.

    • Added the JSON_TABLE() function in MySQL 8.0.4. This function accepts JSON data and returns it as a relational table having the specified columns.

      This function has the syntax JSON_TABLE(expr, path COLUMNS column_list) [AS] alias), where expr is an expression that returns JSON data, path is a JSON path applied to the source, and column_list is a list of column definitions. An example is shown here:

      mysql> SELECT *
          -> FROM
          ->   JSON_TABLE(
          ->     '[{"a":3,"b":"0"},{"a":"3","b":"1"},{"a":2,"b":1},{"a":0},{"b":[1,2]}]',
          ->     "$[*]" COLUMNS(
          ->       rowid FOR ORDINALITY,
          ->       xa INT EXISTS PATH "$.a",
          ->       xb INT EXISTS PATH "$.b",
          ->       sa VARCHAR(100) PATH "$.a",
          ->       sb VARCHAR(100) PATH "$.b",
          ->       ja JSON PATH "$.a",
          ->       jb JSON PATH "$.b"
          ->     )
          ->   ) AS  jt1;
      | rowid | xa   | xb   | sa   | sb   | ja   | jb     |
      |     1 |    1 |    1 | 3    | 0    | 3    | "0"    |
      |     2 |    1 |    1 | 3    | 1    | "3"  | "1"    |
      |     3 |    1 |    1 | 2    | 1    | 2    | 1      |
      |     4 |    1 |    0 | 0    | NULL | 0    | NULL   |
      |     5 |    0 |    1 | NULL | NULL | NULL | [1, 2] |

      The JSON source expression can be any expression that yields a valid JSON document, including a JSON literal, a table column, or a function call that returns JSON such as JSON_EXTRACT(t1, data, '$.post.comments'). For more information, see Section 14.17.6, “JSON Table Functions”.

  • Data type support.  MySQL now supports use of expressions as default values in data type specifications. This includes the use of expressions as default values for the BLOB, TEXT, GEOMETRY, and JSON data types, which previously could not be assigned default values at all. For details, see Section 13.6, “Data Type Default Values”.

  • Optimizer.  These optimizer enhancements were added:

    • MySQL now supports invisible indexes. An invisible index is not used by the optimizer at all, but is otherwise maintained normally. Indexes are visible by default. Invisible indexes make it possible to test the effect of removing an index on query performance, without making a destructive change that must be undone should the index turn out to be required. See Section 10.3.12, “Invisible Indexes”.

    • MySQL now supports descending indexes: DESC in an index definition is no longer ignored but causes storage of key values in descending order. Previously, indexes could be scanned in reverse order but at a performance penalty. A descending index can be scanned in forward order, which is more efficient. Descending indexes also make it possible for the optimizer to use multiple-column indexes when the most efficient scan order mixes ascending order for some columns and descending order for others. See Section 10.3.13, “Descending Indexes”.

    • MySQL now supports creation of functional index key parts that index expression values rather than column values. Functional key parts enable indexing of values that cannot be indexed otherwise, such as JSON values. For details, see Section 15.1.15, “CREATE INDEX Statement”.

    • In MySQL 8.0.14 and later, trivial WHERE conditions arising from constant literal expressions are removed during preparation, rather than later on during optimization. Removal of the condition earlier in the process makes it possible to simplify joins for queries with outer joins having trivial conditions, such as this one:

      SELECT * FROM t1 LEFT JOIN t2 ON condition_1 WHERE condition_2 OR 0 = 1

      The optimizer now sees during preparation that 0 = 1 is always false, making OR 0 = 1 redundant, and removes it, leaving this:

      SELECT * FROM t1 LEFT JOIN t2 ON condition_1 where condition_2

      Now the optimizer can rewrite the query as an inner join, like this:

      SELECT * FROM t1 LEFT JOIN t2 WHERE condition_1 AND condition_2

      For more information, see Section, “Outer Join Optimization”.

    • In MySQL 8.0.16 and later, MySQL can use constant folding at optimization time to handle comparisons between a column and a constant value where the constant is out of range or on a range boundary with respect to the type of the column, rather than doing so for each row at execution time. For example, given a table t with a TINYINT UNSIGNED column c, the optimizer can rewrite a condition such as WHERE c < 256 to WHERE 1 (and optimize the condition away altogether), or WHERE c >= 255 to WHERE c = 255.

      See Section, “Constant-Folding Optimization”, for more information.

    • Beginning with MySQL 8.0.16, the semijoin optimizations used with IN subqueries can now be applied to EXISTS subqueries as well. In addition, the optimizer now decorrelates trivially-correlated equality predicates in the WHERE condition attached to the subquery, so that they can be treated similarly to expressions in IN subqueries; this applies to both EXISTS and IN subqueries.

      For more information, see Section, “Optimizing IN and EXISTS Subquery Predicates with Semijoin Transformations”.

    • As of MySQL 8.0.17, the server rewrites any incomplete SQL predicates (that is, predicates having the form WHERE value, in which value is a column name or constant expression and no comparison operator is used) internally as WHERE value <> 0 during the contextualization phase, so that the query resolver, query optimizer, and query executor need work only with complete predicates.

      One visible effect of this change is that, for Boolean values, EXPLAIN output now shows true and false, rather than 1 and 0.

      Another effect of this change is that evaluation of a JSON value in an SQL boolean context performs an implicit comparison against JSON integer 0. Consider the table created and populated as shown here:

      mysql> CREATE TABLE test (id INT, col JSON);
      mysql> INSERT INTO test VALUES (1, '{"val":true}'), (2, '{"val":false}');

      Previously, the server attempted to convert an extracted true or false value to an SQL boolean when comparing it in an SQL boolean context, as shown by the following query using IS TRUE:

      mysql> SELECT id, col, col->"$.val" FROM test WHERE col->"$.val" IS TRUE;
      | id   | col           | col->"$.val" |
      |    1 | {"val": true} | true         |

      In MySQL 8.0.17 and later, the implicit comparison of the extracted value with JSON integer 0 leads to a different result:

      mysql> SELECT id, col, col->"$.val" FROM test WHERE col->"$.val" IS TRUE;
      | id   | col            | col->"$.val" |
      |    1 | {"val": true}  | true         |
      |    2 | {"val": false} | false        |

      Beginning with MySQL 8.0.21, you can use JSON_VALUE() on the extracted value to perform type conversion prior to performing the test, as shown here:

      mysql> SELECT id, col, col->"$.val" FROM test
          ->     WHERE JSON_VALUE(col, "$.val" RETURNING UNSIGNED) IS TRUE;
      | id   | col           | col->"$.val" |
      |    1 | {"val": true} | true         |

      Also beginning with MySQL 8.0.21, the server provides the warning Evaluating a JSON value in SQL boolean context does an implicit comparison against JSON integer 0; if this is not what you want, consider converting JSON to an SQL numeric type with JSON_VALUE RETURNING when comparing extracted values in an SQL boolean context in this manner.

    • In MySQL 8.0.17 and later a WHERE condition having NOT IN (subquery) or NOT EXISTS (subquery) is transformed internally into an antijoin. (An antijoin returns all rows from the table for which there is no row in the table to which it is joined matching the join condition.) This removes the subquery which can result in faster query execution since the subquery's tables are now handled on the top level.

      This is similar to, and reuses, the existing IS NULL (Not exists) optimization for outer joins; see EXPLAIN Extra Information.

    • Beginning with MySQL 8.0.21, a single-table UPDATE or DELETE statement can now in many cases make use of a semijoin transformation or subquery materialization. This applies to statements of the forms shown here:

      • UPDATE t1 SET t1.a=value WHERE t1.a IN (SELECT t2.a FROM t2)

      • DELETE FROM t1 WHERE t1.a IN (SELECT t2.a FROM t2)

      This can be done for a single-table UPDATE or DELETE meeting the following conditions:

      • The UPDATE or DELETE statement uses a subquery having a [NOT] IN or [NOT] EXISTS predicate.

      • The statement has no ORDER BY clause, and has no LIMIT clause.

        (The multi-table versions of UPDATE and DELETE do not support ORDER BY or LIMIT.)

      • The target table does not support read-before-write removal (relevant only for NDB tables).

      • Semijoin or subquery materialization is allowed, based on any hints contained in the subquery and the value of optimizer_switch.

      When the semijoin optimization is used for an eligible single-table DELETE or UPDATE, this is visible in the optimizer trace: for a multi-table statement there is a join_optimization object in the trace, while there is none for a single-table statement. The conversion is also visible in the output of EXPLAIN FORMAT=TREE or EXPLAIN ANALYZE; a single-table statement shows <not executable by iterator executor>, while a multi-table statement reports a full plan.

      Also beginning with MySQL 8.0.21, semi-consistent reads are supported by multi-table UPDATE statements using InnoDB tables, for transaction isolation levels weaker than REPEATABLE READ.

    • Improved hash join performance.  MySQL 8.0.23 reimplements the hash table used for hash joins, resulting in several improvements in hash join performance. This work includes a fix for an issue (Bug #31516149, Bug #99933) whereby only roughly 2/3 of the memory allocated for the join buffer (join_buffer_size) could actually be used by a hash join.

      The new hash table is generally faster than the old one, and uses less memory for alignment, keys/values, and in scenarios where there are many equal keys. In addition, the server can now free old memory when the size of the hash table increases.

  • Common table expressions.  MySQL now supports common table expressions, both nonrecursive and recursive. Common table expressions enable use of named temporary result sets, implemented by permitting a WITH clause preceding SELECT statements and certain other statements. For more information, see Section 15.2.20, “WITH (Common Table Expressions)”.

    As of MySQL 8.0.19, the recursive SELECT part of a recursive common table expression (CTE) supports a LIMIT clause. LIMIT with OFFSET is also supported. See Recursive Common Table Expressions, for more information.

  • Window functions.  MySQL now supports window functions that, for each row from a query, perform a calculation using rows related to that row. These include functions such as RANK(), LAG(), and NTILE(). In addition, several existing aggregate functions now can be used as window functions (for example, SUM() and AVG()). For more information, see Section 14.20, “Window Functions”.

  • Lateral derived tables.  A derived table now may be preceded by the LATERAL keyword to specify that it is permitted to refer to (depend on) columns of preceding tables in the same FROM clause. Lateral derived tables make possible certain SQL operations that cannot be done with nonlateral derived tables or that require less-efficient workarounds. See Section, “Lateral Derived Tables”.

  • Aliases in single-table DELETE statements.  In MySQL 8.0.16 and later, single-table DELETE statements support the use of table aliases.

  • Regular expression support.  Previously, MySQL used the Henry Spencer regular expression library to support regular expression operators (REGEXP, RLIKE). Regular expression support has been reimplemented using International Components for Unicode (ICU), which provides full Unicode support and is multibyte safe. The REGEXP_LIKE() function performs regular expression matching in the manner of the REGEXP and RLIKE operators, which now are synonyms for that function. In addition, the REGEXP_INSTR(), REGEXP_REPLACE(), and REGEXP_SUBSTR() functions are available to find match positions and perform substring substitution and extraction, respectively. The regexp_stack_limit and regexp_time_limit system variables provide control over resource consumption by the match engine. For more information, see Section 14.8.2, “Regular Expressions”. For information about ways in which applications that use regular expressions may be affected by the implementation change, see Regular Expression Compatibility Considerations.

    One effect of this change is that [a-zA-Z] and [0-9] perform much better in MySQL 8.0 than [[:alpha:]] and [[:digit:]], respectively. Existing applications that use the character classes in pattern matching should be upgraded to use the ranges instead.

  • Internal temporary tables.  The TempTable storage engine replaces the MEMORY storage engine as the default engine for in-memory internal temporary tables. The TempTable storage engine provides efficient storage for VARCHAR and VARBINARY columns. The internal_tmp_mem_storage_engine session variable defines the storage engine for in-memory internal temporary tables. Permitted values are TempTable (the default) and MEMORY. The temptable_max_ram variable defines the maximum amount of memory that the TempTable storage engine can use before data is stored to disk.

  • Logging.  These enhancements were added to improve logging:

    • Error logging was rewritten to use the MySQL component architecture. Traditional error logging is implemented using built-in components, and logging using the system log is implemented as a loadable component. In addition, a loadable JSON log writer is available. For more information, see Section 7.4.2, “The Error Log”.

    • From MySQL 8.0.30, error log components can be loaded implicitly at startup before the InnoDB storage engine is available. This new method of loading error log components loads and enables the components defined by the log_error_services variable.

      Previously, error log components had to be installed first using INSTALL COMPONENT and could only be loaded after InnoDB was fully available, as the list of components to load was read from the mysql.components table, which is an InnoDB table.

      Implicit loading of error log components has these advantages:

      • Log components are loaded earlier in the startup sequence, making logged information available sooner.

      • It helps avoid loss of buffered log information should a failure occur during startup.

      • Loading log components using INSTALL COMPONENT is not required, simplifying error log configuration.

      The explicit method of loading log components using INSTALL COMPONENT remains supported for backward compatibility.

      For more information, see Section, “Error Log Configuration”.

  • Backup lock.  A new type of backup lock permits DML during an online backup while preventing operations that could result in an inconsistent snapshot. The new backup lock is supported by LOCK INSTANCE FOR BACKUP and UNLOCK INSTANCE syntax. The BACKUP_ADMIN privilege is required to use these statements.

  • Replication.  The following enhancements have been made to MySQL Replication:

    • MySQL Replication now supports binary logging of partial updates to JSON documents using a compact binary format, saving space in the log over logging complete JSON documents. Such compact logging is done automatically when statement-based logging is in use, and can be enabled by setting the new binlog_row_value_options system variable to PARTIAL_JSON. For more information, see Partial Updates of JSON Values, as well as the description of binlog_row_value_options.

  • Connection management.  MySQL Server now permits a TCP/IP port to be configured specifically for administrative connections. This provides an alternative to the single administrative connection that is permitted on the network interfaces used for ordinary connections even when max_connections connections are already established. See Section, “Connection Interfaces”.

    MySQL now provides more control over the use of compression to minimize the number of bytes sent over connections to the server. Previously, a given connection was either uncompressed or used the zlib compression algorithm. Now, it is also possible to use the zstd algorithm, and to select a compression level for zstd connections. The permitted compression algorithms can be configured on the server side, as well as on the connection-origination side for connections by client programs and by servers participating in source/replica replication or Group Replication. For more information, see Section 6.2.8, “Connection Compression Control”.

  • Configuration.  The maximum permitted length of host names throughout MySQL has been raised to 255 ASCII characters, up from the previous limit of 60 characters. This applies to, for example, host name-related columns in the data dictionary, mysql system schema, Performance Schema, INFORMATION_SCHEMA, and sys schema; the MASTER_HOST value for the CHANGE MASTER TO statement; the Host column in SHOW PROCESSLIST statement output; host names in account names (such as used in account-management statements and in DEFINER attributes); and host name-related command options and system variables.


    • The increase in permitted host name length can affect tables with indexes on host name columns. For example, tables in the mysql system schema that index host names now have an explicit ROW_FORMAT attribute of DYNAMIC to accommodate longer index values.

    • Some file name-valued configuration settings might be constructed based on the server host name. The permitted values are constrained by the underlying operating system, which may not permit file names long enough to include 255-character host names. This affects the general_log_file, log_error, pid_file, relay_log, and slow_query_log_file system variables and corresponding options. If host name-based values are too long for the OS, explicit shorter values must be provided.

    • Although the server now supports 255-character host names, connections to the server established using the --ssl-mode=VERIFY_IDENTITY option are constrained by maximum host name length supported by OpenSSL. Host name matches pertain to two fields of SSL certificates, which have maximum lengths as follows: Common Name: maximum length 64; Subject Alternative Name: maximum length as per RFC#1034.

  • Plugins.  Previously, MySQL plugins could be written in C or C++. MySQL header files used by plugins now contain C++ code, which means that plugins must be written in C++, not C.

  • C API.  The MySQL C API now supports asynchronous functions for nonblocking communication with the MySQL server. Each function is the asynchronous counterpart to an existing synchronous function. The synchronous functions block if reads from or writes to the server connection must wait. The asynchronous functions enable an application to check whether work on the server connection is ready to proceed. If not, the application can perform other work before checking again later. See C API Asynchronous Interface.

  • Additional target types for casts.  The functions CAST() and CONVERT() now support conversions to types DOUBLE, FLOAT, and REAL. Added in MySQL 8.0.17. See Section 14.10, “Cast Functions and Operators”.

  • JSON schema validation.  MySQL 8.0.17 adds two functions JSON_SCHEMA_VALID() and JSON_SCHEMA_VALIDATION_REPORT() for validating JSON documents again JSON schemas. JSON_SCHEMA_VALID() returns TRUE (1) if the document validates against the schema and FALSE (0) if it does not. JSON_SCHEMA_VALIDATION_REPORT() returns a JSON document containing detailed information about the results of the validation. The following statements apply to both of these functions:

    • The schema must conform to Draft 4 of the JSON Schema specification.

    • required attributes are supported.

    • External resources and the $ref keyword are not supported.

    • Regular expression patterns are supported; invalid patterns are silently ignored.

    See Section 14.17.7, “JSON Schema Validation Functions”, for more information and examples.

  • Multi-valued indexes.  Beginning with MySQL 8.0.17, InnoDB supports the creation of a multi-valued index, which is a secondary index defined on a JSON column that stores an array of values and which can have multiple index records for a single data record. Such an index uses a key part definition such as CAST(data->'$.zipcode' AS UNSIGNED ARRAY). A multi-valued index is used automatically by the MySQL optimizer for suitable queries, as can be viewed in the output of EXPLAIN.

    As part of this work, MySQL adds a new function JSON_OVERLAPS() and a new MEMBER OF() operator for working with JSON documents, additionally extending the CAST() function with a new ARRAY keyword, as described in the following list:

    • JSON_OVERLAPS() compares two JSON documents. If they contain any key-value pairs or array elements in common, the function returns TRUE (1); otherwise it returns FALSE (0). If both values are scalars, the function performs a simple test for equality. If one argument is a JSON array and the other is a scalar, the scalar is treated as an array element. Thus, JSON_OVERLAPS() acts as a complement to JSON_CONTAINS().

    • MEMBER OF() tests whether the first operand (a scalar or JSON document) is a member of the JSON array passed as the second operand, returning TRUE (1) if it is, and FALSE (0) if it is not. No type conversion of the operand is performed.

    • CAST(expression AS type ARRAY) permits creation of a functional index by casting the JSON array found in a JSON document at json_path to an SQL array. Type specifiers are limited to those already supported by CAST(), with the exception of BINARY (not supported). This usage of CAST() (and the ARRAY keyword) is supported only by InnoDB, and only for the creation of a multi-valued index.

    For detailed information about multi-valued indexes, including examples, see Multi-Valued Indexes. Section 14.17.3, “Functions That Search JSON Values”, provides information about JSON_OVERLAPS() and MEMBER OF(), along with examples of use.

  • Hintable time_zone.  As of MySQL 8.0.17, the time_zone session variable is hintable using SET_VAR.

  • Redo Log Archiving.  As of MySQL 8.0.17, InnoDB supports redo log archiving. Backup utilities that copy redo log records may sometimes fail to keep pace with redo log generation while a backup operation is in progress, resulting in lost redo log records due to those records being overwritten. The redo log archiving feature addresses this issue by sequentially writing redo log records to an archive file. Backup utilities can copy redo log records from the archive file as necessary, thereby avoiding the potential loss of data. For more information, see Redo Log Archiving.

  • The Clone Plugin.  As of MySQL 8.0.17, MySQL provides a clone plugin that permits cloning InnoDB data locally or from a remote MySQL server instance. A local cloning operation stores cloned data on the same server or node where the MySQL instance runs. A remote cloning operation transfers cloned data over the network from a donor MySQL server instance to the recipient server or node where the cloning operation was initiated.

    The clone plugin supports replication. In addition to cloning data, a cloning operation extracts and transfers replication coordinates from the donor and applies them on the recipient, which enables using the clone plugin for provisioning Group Replication members and replicas. Using the clone plugin for provisioning is considerably faster and more efficient than replicating a large number of transactions. Group Replication members can also be configured to use the clone plugin as an alternative method of recovery, so that members automatically choose the most efficient way to retrieve group data from seed members.

    For more information, see Section 7.6.7, “The Clone Plugin”, and Section, “Cloning for Distributed Recovery”.

    As of MySQL 8.0.27, concurrent DDL operations on the donor MySQL Server instance are permitted while a cloning operation is in progress. Previously, a backup lock was held during the cloning operation, preventing concurrent DDL on the donor. To revert to the previous behavior of blocking concurrent DDL on the donor during a clone operation, enable the clone_block_ddl variable. See Section, “Cloning and Concurrent DDL”.

    As of MySQL 8.0.29, the clone_delay_after_data_drop variable permits specifying a delay period immediately after removing existing data on the recipient MySQL Server instance at the start of a remote cloning operation. The delay is intended to provide enough time for the file system on the recipient host to free space before data is cloned from the donor MySQL Server instance. Certain file systems free space asynchronously in a background process. On these file systems, cloning data too soon after dropping existing data can result in clone operation failures due to insufficient space. The maximum delay period is 3600 seconds (1 hour). The default setting is 0 (no delay).

    As of MySQL 8.0.37, cloning is allowed between different point releases. In other words, only the major and minor version numbers must match when previously the point release number also had to match.

    For example, clone functionality now permits cloning 8.0.37 to 8.0.41 or 8.0.51 to 8.0.39. Previous restrictions still apply to versions older than 8.0.37, so cloning the likes of 8.0.36 to 8.0.42 or vice-versa is not permitted.

  • Hash Join Optimization.  Beginning with MySQL 8.0.18, a hash join is used whenever each pair of tables in a join includes at least one equi-join condition, and no indexes apply to any join condition. A hash join does not require indexes, although it can be used with indexes applying to single-table predicates only. A hash join is more efficient in most cases than the block-nested loop algorithm. Joins such as those shown here can be optimized in this manner:

    SELECT *
        FROM t1
        JOIN t2
            ON t1.c1=t2.c1;
    SELECT *
        FROM t1
        JOIN t2
            ON (t1.c1 = t2.c1 AND t1.c2 < t2.c2)
        JOIN t3
            ON (t2.c1 = t3.c1)

    Hash joins can also be used for Cartesian products—that is, when no join condition is specified.

    You can see when the hash join optimization is being used for a particular query using EXPLAIN FORMAT=TREE or EXPLAIN ANALYZE. (In MySQL 8.0.20 and later, you can also use EXPLAIN, omitting FORMAT=TREE.)

    The amount of memory available to a hash join is limited by the value of join_buffer_size. A hash join that requires more than this much memory is executed on disk; the number of disk files that can be used by an on-disk hash join is limited by open_files_limit.

    As of MySQL 8.0.19, the hash_join optimizer switch which was introduced in MySQL 8.0.18 no longer supported (hash_join=on still appears as part of the value of optimizer_switch, but setting it no longer has any effect). The HASH_JOIN and NO_HASH_JOIN optimizer hints are also no longer supported. The switch and the hint are both now deprecated; expect them to be removed in a future MySQL release. In MySQL 8.0.18 and later, hash joins can be disabled using the NO_BNL optimizer switch.

    In MySQL 8.0.20 and later, block nested loop is no longer used in the MySQL server, and a hash join is employed any time a block nested loop would have been used previously, even when the query contains no equi-join conditions. This applies to inner non-equijoins, semijoins, antijoins, left outer joins, and right outer joins. The block_nested_loop flag for the optimizer_switch system variable as well as the BNL and NO_BNL optimizer hints are still supported, but henceforth control use of hash joins only. In addition, both inner and outer joins (including semijoins and antijoins) can now employ batched key access (BKA), which allocates join buffer memory incrementally so that individual queries need not use up large amounts of resources that they do not actually require for resolution. BKA for inner joins only is supported starting with MySQL 8.0.18.

    MySQL 8.0.20 also replaces the executor used in previous versions of MySQL with the iterator executor. This work includes replacement of the old index subquery engines that governed queries of the form WHERE value IN (SELECT column FROM table WHERE ...) for those IN queries which have not been optimized as semijoins, as well as queries materialized in the same form, which formerly depended on the old executor.

    For more information and examples, see Section, “Hash Join Optimization”. See also Batched Key Access Joins.

  • EXPLAIN ANALYZE Statement.  A new form of the EXPLAIN statement, EXPLAIN ANALYZE, is implemented in MySQL 8.0.18, providing expanded information about the execution of SELECT statements in TREE format for each iterator used in processing the query, and making it possible to compare estimated cost with the actual cost of the query. This information includes startup cost, total cost, number of rows returned by this iterator, and the number of loops executed.

    In MySQL 8.0.21 and later, this statement also supports a FORMAT=TREE specifier. TREE is the only supported format.

    See Obtaining Information with EXPLAIN ANALYZE, for more information.

  • Query cast injection.  In version 8.0.18 and later, MySQL injects cast operations into the query item tree inside expressions and conditions in which the data type of the argument and the expected data type do not match. This has no effect on query results or speed of execution, but makes the query as executed equivalent to one which is compliant with the SQL standard while maintaining backwards compatibility with previous releases of MySQL.

    Such implicit casts are now performed between temporal types (DATE, DATETIME, TIMESTAMP, TIME) and numeric types (SMALLINT, TINYINT, MEDIUMINT, INT/INTEGER, BIGINT; DECIMAL/NUMERIC; FLOAT, DOUBLE, REAL; BIT) whenever they are compared using any of the standard numeric comparison operators (=, >=, >, <, <=, <>/!=, or <=>). In this case, any value that is not already a DOUBLE is cast as one. Cast injection is also now performed for comparisons between DATE or TIME values and DATETIME values, where the arguments are cast whenever necessary as DATETIME.

    Beginning with MySQL 8.0.21, such casts are also performed when comparing string types with other types. String types that are cast include CHAR, VARCHAR, BINARY, VARBINARY, BLOB, TEXT, ENUM, and SET. When comparing a value of a string type with a numeric type or YEAR, the string cast is to DOUBLE; if the type of the other argument is not FLOAT, DOUBLE, or REAL, it is also cast to DOUBLE. When comparing a string type to a DATETIME or TIMESTAMP value, the string is cast is to DATETIME; when comparing a string type with DATE, the string is cast to DATE.

    It is possible to see when casts are injected into a given query by viewing the output of EXPLAIN ANALYZE, EXPLAIN FORMAT=JSON, or, as shown here, EXPLAIN FORMAT=TREE:

    mysql> CREATE TABLE d (dt DATETIME, d DATE, t TIME);
    Query OK, 0 rows affected (0.62 sec)
    mysql> CREATE TABLE n (i INT, d DECIMAL, f FLOAT, dc DECIMAL);
    Query OK, 0 rows affected (0.51 sec)
    mysql> CREATE TABLE s (c CHAR(25), vc VARCHAR(25),
        ->     bn BINARY(50), vb VARBINARY(50), b BLOB, t TEXT,
        ->     e ENUM('a', 'b', 'c'), se SET('x' ,'y', 'z'));
    Query OK, 0 rows affected (0.50 sec)
    mysql> EXPLAIN FORMAT=TREE SELECT * from d JOIN n ON d.dt = n.i\G
    *************************** 1. row ***************************
    EXPLAIN: -> Inner hash join (cast(d.dt as double) = cast(n.i as double))
    (cost=0.70 rows=1)
        -> Table scan on n  (cost=0.35 rows=1)
        -> Hash
            -> Table scan on d  (cost=0.35 rows=1)
    mysql> EXPLAIN FORMAT=TREE SELECT * from s JOIN d ON d.dt = s.c\G
    *************************** 1. row ***************************
    EXPLAIN: -> Inner hash join (d.dt = cast(s.c as datetime(6)))  (cost=0.72 rows=1)
        -> Table scan on d  (cost=0.37 rows=1)
        -> Hash
            -> Table scan on s  (cost=0.35 rows=1)
    1 row in set (0.01 sec)
    mysql> EXPLAIN FORMAT=TREE SELECT * from n JOIN s ON n.d = s.c\G
    *************************** 1. row ***************************
    EXPLAIN: -> Inner hash join (cast(n.d as double) = cast(s.c as double))  (cost=0.70 rows=1)
        -> Table scan on s  (cost=0.35 rows=1)
        -> Hash
            -> Table scan on n  (cost=0.35 rows=1)
    1 row in set (0.00 sec)

    Such casts can also be seen by executing EXPLAIN [FORMAT=TRADITIONAL], in which case it is also necessary to issue SHOW WARNINGS after executing the EXPLAIN statement.

  • Time zone support for TIMESTAMP and DATETIME.  As of MySQL 8.0.19, the server accepts a time zone offset with inserted datetime (TIMESTAMP and DATETIME) values. This offset uses the same format as that employed when setting the time_zone system variable, except that a leading zero is required when the hours portion of the offset is less than 10, and '-00:00' is not allowed. Examples of datetime literals that include time zone offsets are '2019-12-11 10:40:30-05:00', '2003-04-14 03:30:00+10:00', and '2020-01-01 15:35:45+05:30'.

    Time zone offsets are not displayed when selecting datetime values.

    Datetime literals incorporating time zone offsets can be used as prepared statement parameter values.

    As part of this work, the value used to set the time_zone system variable is now also restricted to the range -13:59 to +14:00, inclusive. (It remains possible to assign name values to time_zone such as 'EST', 'Posix/Australia/Brisbane', and 'Europe/Stockholm' to this variable, provided that the MySQL time zone tables are loaded; see Populating the Time Zone Tables).

    For more information and examples, see Section 7.1.15, “MySQL Server Time Zone Support”, as well as Section 13.2.2, “The DATE, DATETIME, and TIMESTAMP Types”.

  • Precise information for JSON schema CHECK constraint failures.  When using JSON_SCHEMA_VALID() to specify a CHECK constraint, MySQL 8.0.19 and later provides precise information about the reasons for failures of such constraints.

    For examples and more information, see JSON_SCHEMA_VALID() and CHECK constraints. See also Section, “CHECK Constraints”.

  • Row and column aliases with ON DUPLICATE KEY UPDATE.  Beginning with MySQL 8.0.19, it is possible to reference the row to be inserted, and, optionally, its columns, using aliases. Consider the following INSERT statement on a table t having columns a and b:

    INSERT INTO t SET a=9,b=5

    Using the alias new for the new row, and, in some cases, the aliases m and n for this row's columns, the INSERT statement can be rewritten in many different ways, some examples of which are shown here:

    INSERT INTO t SET a=9,b=5 AS new
        ON DUPLICATE KEY UPDATE a=new.a+new.b;
    INSERT INTO t VALUES(9,5) AS new
        ON DUPLICATE KEY UPDATE a=new.a+new.b;
    INSERT INTO t SET a=9,b=5 AS new(m,n)
    INSERT INTO t VALUES(9,5) AS new(m,n)

    For more information and examples, see Section, “INSERT ... ON DUPLICATE KEY UPDATE Statement”.

  • SQL standard explicit table clause and table value constructor.  Added table value constructors and explicit table clauses according to the SQL standard. These are implemented in MySQL 8.0.19, respectively, as the TABLE statement and the VALUES statement.

    The TABLE statement has the format TABLE table_name, and is equivalent to SELECT * FROM table_name. It supports ORDER BY and LIMIT clauses ( the latter with optional OFFSET), but does not allow for the selection of individual table columns. TABLE can be used anywhere that you would employ the equivalent SELECT statement; this includes joins, unions, INSERT ... SELECT, REPLACE, CREATE TABLE ... SELECT statements, and subqueries. For example:

    • TABLE t1 UNION TABLE t2 is equivalent to SELECT * FROM t1 UNION SELECT * FROM t2

    • CREATE TABLE t2 TABLE t1 is equivalent to CREATE TABLE t2 SELECT * FROM t1

    • SELECT a FROM t1 WHERE b > ANY (TABLE t2) is equivalent to SELECT a FROM t1 WHERE b > ANY (SELECT * FROM t2).

    VALUES can be used to supply a table value to an INSERT, REPLACE, or SELECT statement, and consists of the VALUES keyword followed by a series of row constructors (ROW()) separated by commas. For example, the statement INSERT INTO t1 VALUES ROW(1,2,3), ROW(4,5,6), ROW(7,8,9) provides an SQL-compliant equivalent to the MySQL-specific INSERT INTO t1 VALUES (1,2,3), (4,5,6), (7,8,9). You can also select from a VALUES table value constructor just as you would a table, bearing in mind that you must supply a table alias when doing so, and use this SELECT just as you would any other; this includes joins, unions, and subqueries.

    For more information about TABLE and VALUES, and for examples of their use, see the following sections of this documentation:

  • Optimizer hints for FORCE INDEX, IGNORE INDEX.  MySQL 8.0 introduces index-level optimizer hints which serve as analogs to the traditional index hints as described in Section 10.9.4, “Index Hints”. The new hints are listed here, along with their FORCE INDEX or IGNORE INDEX equivalents:

    For example, the following two queries are equivalent:

    SELECT /*+ JOIN_INDEX(t1 i_a) */ a FROM t1 WHERE a=1 AND b=2;

    The optimizer hints listed previously follow the same basic rules for syntax and usage as existing index-level optimizer hints.

    These optimizer hints are intended to replace FORCE INDEX and IGNORE INDEX, which we plan to deprecate in a future MySQL release, and subsequently to remove from MySQL. They do not implement a single exact equivalent for USE INDEX; instead, you can employ one or more of NO_INDEX, NO_JOIN_INDEX, NO_GROUP_INDEX, or NO_ORDER_INDEX to achieve the same effect.

    For further information and examples of use, see Index-Level Optimizer Hints.

  • JSON_VALUE() function.  MySQL 8.0.21 implements a new function JSON_VALUE() intended to simplify indexing of JSON columns. In its most basic form, it takes as arguments a JSON document and a JSON path pointing to a single value in that document, as well as (optionally) allowing you to specify a return type with the RETURNING keyword. JSON_VALUE(json_doc, path RETURNING type) is equivalent to this:

        JSON_UNQUOTE( JSON_EXTRACT(json_doc, path) )
        AS type

    You can also specify ON EMPTY, ON ERROR, or both clauses, similar to those employed with JSON_TABLE().

    You can use JSON_VALUE() to create an index on an expression on a JSON column like this:

        j JSON,
        INDEX i1 ( (JSON_VALUE(j, '$.id' RETURNING UNSIGNED)) )
    INSERT INTO t1 VALUES ROW('{"id": "123", "name": "shoes", "price": "49.95"}');

    A query using this expression, such as that shown here, can make use of the index:

    SELECT j->"$.name" as name, j->"$.price" as price 
        FROM t1

    In many cases, this is simpler than creating a generated column from the JSON column and then creating an index on the generated column.

    For more information and examples, see the description of JSON_VALUE().

  • User comments and user attributes.  MySQL 8.0.21 introduces the ability to set user comments and user attributes when creating or updating user accounts. A user comment consists of arbitrary text passed as the argument to a COMMENT clause used with a CREATE USER or ALTER USER statement. A user attribute consists of data in the form of a JSON object passed as the argument to an ATTRIBUTE clause used with either of these two statements. The attribute can contain any valid key-value pairs in JSON object notation. Only one of COMMENT or ATTRIBUTE can be used in a single CREATE USER or ALTER USER statement.

    User comments and user attributes are stored together internally as a JSON object, the comment text as the value of an element having comment as its key. This information can be retrieved from the ATTRIBUTE column of the Information Schema USER_ATTRIBUTES table; since it is in JSON format, you can use MySQL's JSON function and operators to parse its contents (see Section 14.17, “JSON Functions”). Successive changes to the user attribute are merged with its current value as when using the JSON_MERGE_PATCH() function.


    mysql> CREATE USER 'mary'@'localhost' COMMENT 'This is Mary Smith\'s account';
    Query OK, 0 rows affected (0.33 sec)
    mysql> ALTER USER 'mary'@'localhost'
        -≫     ATTRIBUTE '{"fname":"Mary", "lname":"Smith"}';
    Query OK, 0 rows affected (0.14 sec)
    mysql> ALTER USER 'mary'@'localhost'
        -≫     ATTRIBUTE '{"email":""}';
    Query OK, 0 rows affected (0.12 sec)
    mysql> SELECT
        ->    USER,
        ->    HOST,
        ->    ATTRIBUTE->>"$.fname" AS 'First Name',
        ->    ATTRIBUTE->>"$.lname" AS 'Last Name',
        ->    ATTRIBUTE->>"$.email" AS 'Email',
        ->    ATTRIBUTE->>"$.comment" AS 'Comment'
        -> WHERE USER='mary' AND HOST='localhost'\G
    *************************** 1. row ***************************
          USER: mary
          HOST: localhost
    First Name: Mary
     Last Name: Smith
       Comment: This is Mary Smith's account
    1 row in set (0.00 sec)

    For more information and examples, see Section, “CREATE USER Statement”, Section, “ALTER USER Statement”, and Section 28.3.46, “The INFORMATION_SCHEMA USER_ATTRIBUTES Table”.

  • New optimizer_switch flags.  MySQL 8.0.21 adds two new flags for the optimizer_switch system variable, as described in the following list:

    • prefer_ordering_index flag

      By default, MySQL attempts to use an ordered index for any ORDER BY or GROUP BY query that has a LIMIT clause, whenever the optimizer determines that this would result in faster execution. Because it is possible in some cases that choosing a different optimization for such queries actually performs better, it is now possible to disable this optimization by setting the prefer_ordering_index flag to off.

      The default value for this flag is on.

    • subquery_to_derived flag

      When this flag is set to on, the optimizer transforms eligible scalar subqueries into joins on derived tables. For example, the query SELECT * FROM t1 WHERE t1.a > (SELECT COUNT(a) FROM t2) is rewritten as SELECT t1.a FROM t1 JOIN ( SELECT COUNT(t2.a) AS c FROM t2 ) AS d WHERE t1.a > d.c.

      This optimization can be applied to a subquery which is part of a SELECT, WHERE, JOIN, or HAVING clause; contains one or more aggregate functions but no GROUP BY clause; is not correlated; and does not use any nondeterministic functions.

      The optimization can also be applied to a table subquery which is the argument to IN, NOT IN, EXISTS, or NOT EXISTS, and which does not contain a GROUP BY. For example, the query SELECT * FROM t1 WHERE t1.b < 0 OR t1.a IN (SELECT t2.a + 1 FROM t2) is rewritten as SELECT a, b FROM t1 LEFT JOIN (SELECT DISTINCT 1 AS e1, t2.a AS e2 FROM t2) d ON t1.a + 1 = d.e2 WHERE t1.b < 0 OR d.e1 IS NOT NULL.

      Starting with MySQL 8.0.24, this optimization can also be applied to a correlated scalar subquery by applying an extra grouping to it, and then an outer join on the lifted predicate. For example, a query such as SELECT * FROM t1 WHERE (SELECT a FROM t2 WHERE t2.a=t1.a) > 0 can be rewritten as SELECT t1.* FROM t1 LEFT OUTER JOIN (SELECT a, COUNT(*) AS ct FROM t2 GROUP BY a) AS derived ON t1.a = derived.a WHERE derived.a > 0. MySQL performs a cardinality check to make sure that the subquery does not return more than one row (ER_SUBQUERY_NO_1_ROW). See Section, “Correlated Subqueries”, for more information.

      This optimization is normally disabled, since it does not yield a noticeable performance benefit in most cases; the flag is set to off by default.

    For more information, see Section 10.9.2, “Switchable Optimizations”. See also Section, “LIMIT Query Optimization”, Section, “Optimizing IN and EXISTS Subquery Predicates with Semijoin Transformations”, and Section, “Optimizing Derived Tables, View References, and Common Table Expressions with Merging or Materialization”.

  • XML enhancements.  As of MySQL 8.0.21, the LOAD XML statement now supports CDATA sections in the XML to be imported.

  • Casting to the YEAR type now supported.  Beginning with MySQL 8.0.22, the server allows casting to YEAR. Both the CAST() and CONVERT() functions support single-digit, two-digit, and four-digit YEAR values. For one-digit and two-digit values, the allowed range is 0-99. Four-digit values must be in the range 1901-2155. YEAR can also be used as the return type for the JSON_VALUE() function; this function supports four-digit years only.

    String, time-and-date, and floating-point values can all be cast to YEAR. Casting of GEOMETRY values to YEAR is not supported.

    For more information, including conversion rules, see the description of the CONVERT() function.

  • Retrieval of TIMESTAMP values as UTC.  MySQL 8.0.22 and later supports conversion of a TIMESTAMP column value from the system time zone to a UTC DATETIME on retrieval, using CAST(value AT TIME ZONE specifier AS DATETIME), where the specifier is one of [INTERVAL] '+00:00' or 'UTC'. The precision of the DATETIME value returned by the cast can be specified up to 6 decimal places, if desired. The ARRAY keyword is not supported with this construct.

    TIMESTAMP values inserted into a table using a timezone offset are also supported. Use of AT TIME ZONE is not supported for CONVERT() or any other MySQL function or construct.

    For further information and examples, see the description of the CAST() function.

  • Dump file output synchronization.  MySQL 8.0.22 and later supports periodic synchronization when writing to files by SELECT INTO DUMPFILE and SELECT INTO OUTFILE statements. This can be enabled by setting the select_into_disk_sync system variable to ON; the size of the write buffer is determined by the value set for select_into_buffer_size; the default is 131072 (217) bytes.

    In addition, an optional delay following synchronization to disk can be set using select_into_disk_sync_delay; the default is no delay (0 milliseconds).

    For more information, see the descriptions of the variables referenced previously in this item.

  • Single preparation of statements.  As of MySQL 8.0.22, a prepared statement is prepared a single time, rather than once each time it is executed. This is done when executing PREPARE. This is also true for any statement inside a stored procedure; the statement is prepared once, when the stored procedure is first executed.

    One result of this change is that the fashion in which dynamic parameters used in prepared statements are resolved is also changed in the ways listed here:

    • A prepared statement parameter is assigned a data type when the statement is prepared; the type persists for each subsequent execution of the statement (unless the statement is reprepared; see following).

      Using a different data type for a given parameter or user variable within a prepared statement for executions of the statement subsequent to the first execution may cause the statement to be reprepared; for this reason, it is advisable to use the same data type for a given parameter when re-executing a prepared statement.

    • The following constructs employing window functions are no longer accepted, in order to align with the SQL standard:

      This facilitates greater compliance with the SQL standard. See the individual function descriptions for further details.

    • A user variable referenced within a prepared statement now has its data type determined when the statement is prepared; the type persists for each subsequent execution of the statement.

    • A user variable referenced by a statement occurring within a stored procedure now has its data type determined the first time the statement is executed; the type persists for any subsequent invocation of the containing stored procedure.

    • When executing a prepared statement of the form SELECT expr1, expr2, ... FROM table ORDER BY ?, passing an integer value N for the parameter no longer causes ordering of the results by the Nth expression in the select list; the results are no longer ordered, as is expected with ORDER BY constant.

    Preparing a statement used as a prepared statement or within a stored procedure only once enhances the performance of the statement, since it negates the added cost of repeated preparation. Doing so also avoids possible multiple rollbacks of preparation structures, which has been the source of numerous issues in MySQL.

    For more information, see Section 15.5.1, “PREPARE Statement”.

  • RIGHT JOIN as LEFT JOIN handling.  As of MySQL 8.0.22, the server handles all instances of RIGHT JOIN internally as LEFT JOIN, eliminating a number of special cases in which a complete conversion was not performed at parse time.

  • Derived condition pushdown optimization.  MySQL 8.0.22 (and later) implements derived condition pushdown for queries having materialized derived tables. For a query such as SELECT * FROM (SELECT i, j FROM t1) AS dt WHERE i > constant, it is now possible in many cases to push the outer WHERE condition down to the derived table, in this case resulting in SELECT * FROM (SELECT i, j FROM t1 WHERE i > constant) AS dt.

    Previously, if the derived table was materialized and not merged, MySQL materialized the entire table, then qualified the rows with the WHERE condition. Moving the WHERE condition into the subquery using the derived condition pushdown optimization can often reduce the number of rows must be processed, which can decrease the time needed to execute the query.

    An outer WHERE condition can be pushed down directly to a materialized derived table when the derived table does not use any aggregate or window functions. When the derived table has a GROUP BY and does not use any window functions, the outer WHERE condition can be pushed down to the derived table as a HAVING condition. The WHERE condition can also be pushed down when the derived table uses a window function and the outer WHERE references columns used in the window function's PARTITION clause.

    Derived condition pushdown is enabled by default, as indicated by the optimizer_switch system variable's derived_condition_pushdown flag. The flag, added in MySQL 8.0.22, is set to on by default; to disable the optimization for a specific query, you can use the NO_DERIVED_CONDITION_PUSHDOWN optimizer hint (also added in MySQL 8.0.22). If the optimization is disabled due to derived_condition_pushdown being set to off, you can enable it for a given query using DERIVED_CONDITION_PUSHDOWN.

    The derived condition pushdown optimization cannot be employed for a derived table that contains a LIMIT clause. Prior to MySQL 8.0.29, the optimization also cannot be used when the query contains UNION. In MySQL 8.0.29 and later, conditions can be pushed down to both query blocks of a union in most cases; see Section, “Derived Condition Pushdown Optimization”, for more information.

    In addition, a condition that itself uses a subquery cannot be pushed down, and a WHERE condition cannot be pushed down to a derived table that is also an inner table of an outer join. For additional information and examples, see Section, “Derived Condition Pushdown Optimization”.

  • Non-locking reads on MySQL grant tables.  As of MySQL 8.0.22, to permit concurrent DML and DDL operations on MySQL grant tables, read operations that previously acquired row locks on MySQL grant tables are executed as non-locking reads.

    The operations that are now performed as non-locking reads on MySQL grant tables include:

    • SELECT statements and other read-only statements that read data from grant tables through join lists and subqueries, including SELECT ... FOR SHARE statements, using any transaction isolation level.

    • DML operations that read data from grant tables (through join lists or subqueries) but do not modify them, using any transaction isolation level.

    For additional information, see Grant Table Concurrency.

  • 64-bit support for FROM_UNIXTIME(), UNIX_TIMESTAMP(), CONVERT_TZ().  As of MySQL 8.0.28, the functions FROM_UNIXTIME(), UNIX_TIMESTAMP(), and CONVERT_TZ() handle 64-bit values on platforms that support them. This includes 64-bit versions of Linux, MacOS, and Windows.

    On compatible platforms, UNIX_TIMESTAMP() now handles values up to '3001-01-18 23:59:59.999999' UTC, and FROM_UNIXTIME() can convert values up to 32536771199.999999 seconds since the Unix Epoch; CONVERT_TZ() now accepts values that do not exceed '3001-01-18 23:59:59.999999' UTC following conversion.

    The behavior of these functions on 32-bit platforms is unaffected by these changes. The behavior of the TIMESTAMP type is also not affected (on any platform); for working with datetimes after '2038-01-19 03:14:07.999999', UTC, use the DATETIME type instead.

    For more information, see the descriptions of the individual functions just discussed, in Section 14.7, “Date and Time Functions”.

  • Resource allocation control.  Beginning with MySQL 8.0.28, you can see the amount of memory used for queries issued by all regular users by checking the Global_connection_memory status variable. (This total does not include resources used by system users such as MySQL root. It is also exclusive of any memory taken by the InnoDB buffer pool.)

    To enable updates of Global_connection_memory, it is necessary to set global_connection_memory_tracking = 1; this is 0 (off) by default. You can control how often Global_connection_memory is updated by setting connection_memory_chunk_size.

    It is also possible to set memory usage limits for normal users on the session or global level, or both, by setting either or both of the system variables listed here:

    • connection_memory_limit: Amount of memory allocated for each connection. Whenever this limit is exceeded for any user, new queries from this user are rejected.

    • global_connection_memory_limit: Amount of memory allocated for all connections. Whenever this limit is exceeded, new queries from any regular user are rejected.

    These limits do not apply to system processes or administrative accounts.

    See the descriptions of the referenced variables for more information.

  • Detached XA transactions.  MySQL 8.0.29 adds support for XA transactions which, once prepared, are no longer connected to the originating connection. This means that they can be committed or rolled back by another connection, and that the current session can immediately begin another transaction.

    A system variable xa_detach_on_prepare controls whether XA transaction are detached; the default is ON, which causes all XA transactions to be detached. Use of temporary tables is disallowed for XA transactions when this is in effect.

    For more information, see Section, “XA Transaction States”.

  • Automatic binary log purge control.  MySQL 8.0.29 adds the binlog_expire_logs_auto_purge system variable, which provides a single interface for enabling and disabling automatic purging of the binary logs. This is enabled (ON) by default; to disable automatic purging of the binary log files, set this variable to OFF.

    binlog_expire_logs_auto_purge must be ON in order for automatic purging of the binary log files to proceed; the value of this variable takes precedence over that of any other server option or variable, including (but not exclusive to) binlog_expire_logs_seconds.

    The setting for binlog_expire_logs_auto_purge has no effect on PURGE BINARY LOGS.

  • Conditional routine and trigger creation statements.  Beginning with MySQL 8.0.29, the following statements support an IF NOT EXISTS option:

    For CREATE FUNCTION when creating a stored function and CREATE PROCEDURE, this option prevents an error from occurring if there is already a routine having the same name. For CREATE FUNCTION when used to create a loadable function, the option prevents an error if there already exists a loadable function having that name. For CREATE TRIGGER, the option prevents an error from occurring if there already exists in the same schema and on the same table a trigger having the same name.

    This enhancement aligns the syntax of these statements more closely with that of CREATE DATABASE, CREATE TABLE, CREATE USER, and CREATE EVENT (all of which already support IF NOT EXISTS), and acts to complement the IF EXISTS option supported by DROP PROCEDURE, DROP FUNCTION, and DROP TRIGGER statements.

    For more information, see the descriptions of the indicated SQL statements, as well as Function Name Resolution. See also Section, “Replication of CREATE TABLE ... SELECT Statements”.

  • Included FIDO library upgrade.  MySQL 8.0.30 upgrades the included fido2 library (used with the authentication_fido plugin) from version 1.5.0 to version 1.8.0.

    See Section, “FIDO Pluggable Authentication”, for more information.

  • Character sets: Language-specific collations.  Previously, when more than one language had the exact same collation definition, MySQL implemented collations for only one of the languages, which meant that some languages were covered only by utf8mb4 Unicode 9.0 collations specific to other languages. MySQL 8.0.30 (and later) fixes such issues by providing language-specific collations for those languages that were previously covered only by language-specific collations for other languages. Languages covered by the new collations are listed here:

    • Norwegian (Nynorsk)


      Norwegian (Bokmål)

    • Serbian (Latin characters)

    • Bosnian (Latin characters)

    • Bulgarian

    • Galician

    • Mongolian (Cyrillic characters)

    MySQL provides *_as_cs and *_ai_ci collations for each of the languages just listed.

    For more information, see Language-Specific Collations.

  • IF EXISTS and IGNORE UNKNOWN USER options for REVOKE.  MySQL 8.0.30 implements two new options for REVOKE which can be used to determine whether a statement yields an error or a warning when a user, role, or privilege specified in the statement cannot be found, or cannot be assigned. Very basic syntax showing the placement of these new options is provided here:

    REVOKE [IF EXISTS] privilege_or_role 
        ON object 
        FROM user_or_role [IGNORE UNKNOWN USER]

    IF EXISTS causes an unsuccessful REVOKE statement to raise a warning instead of an error, as long as the named target user or role actually exists, despite any references in the statement to any roles or privileges which cannot be found.

    IGNORE UNKNOWN USER causes an unsuccessful REVOKE to raise a warning rather than an error when the target user or role named in the statement cannot be found.

    For further information and examples, see Section, “REVOKE Statement”.

  • Generated invisible primary keys.  Beginning with MySQL 8.0.30, it is possible to run a replication source server such that a generated invisible primary key (GIPK) is added to any InnoDB table that is created without an explicit primary key. The generated key column definition added to such a table is equivalent to what is shown here:


    GIPK mode is not enabled by default. To enable it, set the sql_generate_invisible_primary_key server system variable to ON.

    Generated invisible primary keys are normally visible in the output of statements such as SHOW CREATE TABLE and SHOW INDEX, as well as in MySQL Information Schema tables such as the COLUMNS and STATISTICS tables. You can cause them to be hidden in such cases instead, by setting show_gipk_in_create_table_and_information_schema to OFF.

    As part of this work, a new --skip-generated-invisible-primary-key option is added to mysqldump and mysqlpump to exclude generated invisible primary keys, columns, and column values from their output.

    GIPKs and replication between tables with or without primary keys.  In MySQL Replication, a replica effectively ignores any setting for sql_generate_invisible_primary_key on the source, such that it has no effect on replicated tables. MySQL 8.0.32 and later makes it possible for the replica to add a generated invisible primary key to any InnoDB table that otherwise, as replicated, has no primary key. You can do this by invoking CHANGE REPLICATION SOURCE TO ... REQUIRE_TABLE_PRIMARY_KEY_CHECK = GENERATE on the replica.

    REQUIRE_TABLE_PRIMARY_KEY_CHECK = GENERATE is not compatible with MySQL Group Replication.

    For further information, see Section, “Generated Invisible Primary Keys”.

  • Crash-safe XA transactions.  Previously, XA transactions were not fully resilient to an unexpected halt with respect to the binary log, and if this occurred while the server was executing XA PREPARE, XA COMMIT, or XA ROLLBACK, the server was not guaranteed to be recoverable to the correct state, possibly leaving the binary log with extra XA transactions that had not been applied, or missing one or more XA transactions that had been applied. Beginning with MySQL 8.0.30, this is no longer an issue, and a server that drops out of a replication topology for whatever reason can always be brought back to a consistent XA transaction state when rejoining.

    Known issue: When the same transaction XID is used to execute XA transactions sequentially and a break occurs during the execution of XA COMMIT ... ONE PHASE, using this same XID, after this transaction has been prepared in the storage engine, it may not be possible any longer to synchronize the state between the binary log and the storage engine.

    For more information, see Section, “Restrictions on XA Transactions”.

  • Nesting with UNION.  Beginning with MySQL 8.0.31, bodies of parenthesized query expressions can be nested up to 63 levels deep in combination with UNION. Such queries were previously rejected with error ER_NOT_SUPPORTED_YET, but are now allowed. EXPLAIN output for such a query is shown here:

        ->   (SELECT a, b, c FROM t ORDER BY a LIMIT 3) ORDER BY b LIMIT 2
        -> ) ORDER BY c LIMIT 1\G
    *************************** 1. row ***************************
    EXPLAIN: -> Limit: 1 row(s)  (cost=5.55..5.55 rows=1)
        -> Sort: c, limit input to 1 row(s) per chunk  (cost=2.50 rows=0)
            -> Table scan on <result temporary>  (cost=2.50 rows=0)
                -> Temporary table  (cost=5.55..5.55 rows=1)
                    -> Limit: 2 row(s)  (cost=2.95..2.95 rows=1)
                        -> Sort: b, limit input to 2 row(s) per chunk  (cost=2.50 rows=0)
                            -> Table scan on <result temporary>  (cost=2.50 rows=0)
                                -> Temporary table  (cost=2.95..2.95 rows=1)
                                    -> Limit: 3 row(s)  (cost=0.35 rows=1)
                                        -> Sort: t.a, limit input to 3 row(s) per chunk  (cost=0.35 rows=1)
                                            -> Table scan on t  (cost=0.35 rows=1)
    1 row in set (0.00 sec)

    MySQL follows SQL standard semantics when collapsing bodies of parenthesized query expressions, so that a higher outer limit cannot override an inner lower one. For example, (SELECT ... LIMIT 5) LIMIT 10 can return no more than five rows.

    The 63-level limit is imposed only after the MySQL Optimizer's parser has performed any simplifications or merges which it can.

    For more information, see Section 15.2.11, “Parenthesized Query Expressions”.

  • Disabling query rewrites.  Previously, when using the Rewriter plugin, all queries were subject to being rewritten, regardless of user. This could be problematic in certain cases, such as when administering the system, or when applying statements originating from a replication source or a dump file created by mysqldump or another MySQL program. MySQL 8.0.31 provides a solution to such issues by implementing a new user privilege SKIP_QUERY_REWRITE; statements issued by a user having this privilege are ignored by Rewriter and not rewritten.

    MySQL 8.0.31 also adds a new server system variable rewriter_enabled_for_threads_without_privilege_checks. When set to OFF, rewritable statements issued by threads for which PRIVILEGE_CHECKS_USER is NULL (such as replication applier threads) are not rewritten by the Rewriter plugin. The default is ON, which means such statements are rewritten.

    For more information, see Section 7.6.4, “The Rewriter Query Rewrite Plugin”.

  • Replication filtering of XA statements.  Previously, the statements XA START, XA END, XA COMMIT, and XA ROLLBACK were filtered by the default database whenever using --replicate-do-db or --replicate-ignore-db, which could lead to missed transactions. As of MySQL 8.0.31, these statements are not filtered in such cases, regardless of the value of binlog_format.

  • Replication filtering and privilege checks.  Beginning with MySQL 8.0.31, when replication filtering is in use, a replica no longer raises replication errors related to privilege checks or require_row_format validation for events which are filtered out, making it possible to filter out any transactions that fail validation.

    Because privilege checks on filtered rows can no longer cause replication to stop, a replica can now accept only the portion of a database to which a given user has been granted access; this is true as long as updates to this part of the database are replicated only in row-based format.

    This capability may also be of use when migrating to MySQL HeatWave Service from an on-premise or cloud service which uses tables for administration or other purposes to which the inbound replication user does not have access.

    For more information, see Section 19.2.5, “How Servers Evaluate Replication Filtering Rules”, as well as Section, “Replica Errors During Replication”.

  • INTERSECT and EXCEPT table operators.  MySQL 8.0.31 adds support for the SQL INTERSECT and EXCEPT table operators. Where a and b represent result sets of queries, these operators behave as follows:

    • a INTERSECT b includes only rows appearing in both result sets a and b.

    • a EXCEPT b returns only those rows from result set a which do not also appear in b.

    INTERSECT DISTINCT, INTERSECT ALL, EXCEPT DISTINCT, and EXCEPT ALL are all supported; DISTINCT is the default for both INTERSECT and EXCEPT (this is the same as for UNION).

    For more information and examples, see Section 15.2.8, “INTERSECT Clause”, and Section 15.2.4, “EXCEPT Clause”.

  • User-defined histograms.  Beginning with MySQL 8.0.31, it is possible to set the histogram of a column to a user-specified JSON value. This can be done using the following SQL syntax:

    ANALYZE TABLE tbl_name 
      UPDATE HISTOGRAM ON col_name
      USING DATA 'json_data'

    This statement creates or overwrites a histogram for column col_name of table tbl_name using the histogram's JSON representation json_data. After executing this statement, you can verify that the histogram was created or updated by querying the Information Schema COLUMN_STATISTICS table, like this:

      WHERE TABLE_NAME='tbl_name' 
      AND COLUMN_NAME='col_name';

    The column value returned should be the same json_data used in the previous ANALYZE TABLE statement.

    This can be of use in cases where values deemed important are missed by the histogram sampling process. When this happens, you may want to modify the histogram or set your own histogram based on the complete data set. In addition, sampling a large user data set and building a histogram from it are resource-heavy operations which can impact user queries. With this enhancement, histogram generation can be moved off the (primary) server and performed on a replica instead; the generated histograms can then be assigned to the proper table columns on the source server.

    For more information and examples, see Histogram Statistics Analysis.

  • Server build ID (Linux).  MySQL 8.0.31 adds the read-only build_id system variable for Linux systems, where a 160-bit SHA1 signature is generated at compile time; the value of build_id is that of the generated value converted to a hexadecimal string, providing a unique identifier for the build.

    build_id is written to the server log each time MySQL starts.

    If you build MySQL from source, you can observe that this value changes each time you recompile the server. See Section 2.8, “Installing MySQL from Source”, for more information.

    This variable is not supported on platforms other than Linux.

  • Default EXPLAIN output format.  MySQL 8.0.32 adds a system variable explain_format which determines the format of the output from an EXPLAIN statement used to obtain a query execution plan in the absence of any FORMAT option. For example, if the value of explain_format is TREE, then the output from any such EXPLAIN uses the tree-like format, just as if the statement had specified FORMAT=TREE.

    This behavior is overridden by the value set in a FORMAT option. Suppose that explain_format is set to TREE; even so, EXPLAIN FORMAT=JSON stmt displays the result using the JSON output format.

    For more information and examples, see the description of the explain_format system variable, as well as Obtaining Execution Plan Information. There are also implications for the behavior of EXPLAIN ANALYZE; see Obtaining Information with EXPLAIN ANALYZE.

  • ST_TRANSFORM() Cartesian SRS support.  Prior to MySQL 8.0.30, the ST_TRANSFORM() function did not support Cartesian Spatial Reference Systems. In MySQL 8.0.30 and later, this function provides support for the Popular Visualisation Pseudo Mercator (EPSG 1024) projection method, used for WGS 84 Pseudo-Mercator (SRID 3857). MySQL 8.0.32 and later supports all Cartesian SRSs, except for EPSG 1042, EPSG 1043, EPSG 9816, and EPSG 9826.

Features Deprecated in MySQL 8.0

The following features are deprecated in MySQL 8.0 and may be removed in a future series. Where alternatives are shown, applications should be updated to use them.

For applications that use features deprecated in MySQL 8.0 that have been removed in a higher MySQL series, statements may fail when replicated from a MySQL 8.0 source to a higher-series replica, or may have different effects on source and replica. To avoid such problems, applications that use features deprecated in 8.0 should be revised to avoid them and use alternatives when possible.

  • Wildcard characters in database grants.  The use of the characters % and _ as wildcards in database grants is deprecated as of MySQL 8.0.35. You should expect for the wildcard functionality to removed in a future MySQL release and for these characters always to be treated as literals, as they are already whenever the value of the partial_revokes server system variable is ON.

    In addition, the treatment of % by the server as a synonym for localhost when checking privileges is now also deprecated as of MySQL 8.0.35, and thus subject to removal in a future version of MySQL.

  • Pluggable FIDO authentication is deprecated in MySQL 8.0.35 and later.

  • The --character-set-client-handshake option, originally intended for use with upgrades from very old versions of MySQL, is now deprecated in MySQL 8.0.35 and later MySQL 8.0 releases, where a warning is issued whenever it is used. You should expect this option to be removed in a future version of MySQL; applications depending on this option should begin migration away from it as soon as possible.

  • The old and new server system variables and related server options are deprecated in MySQL 8.0, beginning with MySQL 8.0.35. A warning is now issued whenever either of these variables is set or read. Because these variables are destined for removal in a future version of MySQL, applications which depend on them should begin migration away from them as soon as possible.

  • Legacy audit log filtering mode is deprecated as of MySQL 8.0.34. New deprecation warnings are emitted for legacy audit log filtering system variables. These deprecated variables are either read-only or dynamic.

    (Read-only) audit_log_policy now writes a warning message to the MySQL server error log during server startup when the value is not ALL (default value).

    (Dynamic) audit_log_include_accounts, audit_log_exclude_accounts, audit_log_statement_policy, and audit_log_connection_policy. Dynamic variables print a warning message based on usage:

    • Passing in a non-NULL value to audit_log_include_accounts or audit_log_exclude_accounts during MySQL server startup now writes a warning message to the server error log.

    • Passing in a non-default value to audit_log_statement_policy or audit_log_connection_policy during MySQL server startup now writes a warning message to the server error log. ALL is the default value for both variables.

    • Changing an existing value using SET syntax during a MySQL client session now writes a warning message to the client log.

    • Persisting a variable using SET PERSIST syntax during a MySQL client session now writes a warning message to the client log.

  • In MySQL 8.0.34 and later, the mysql_native_password authentication plugin is deprecated and it now produces a deprecation warning in the server error log if an account attempts to authenticate using mysql_native_password as an authentication method.

  • The ssl_fips_mode server system variable, --ssl-fips-mode client option, and the MYSQL_OPT_SSL_FIPS_MODE option are deprecated and subject to removal in a future version of MySQL.

  • The keyring_file and keyring_encrypted_file plugins are deprecated as of MySQL 8.0.34. These keyring plugins are superseded by the component_keyring_file and component_keyring_encrypted_file components. For a concise comparison of keyring components and plugins, see Section, “Keyring Components Versus Keyring Plugins”.

  • As of MySQL 8.0.31, the keyring_oci plugin is deprecated and subject to removal in a future release of MySQL. Instead, consider using the component_keyring_oci component for storing keyring data (see Section, “Using the Oracle Cloud Infrastructure Vault Keyring Component”).

  • The utf8mb3 character set is deprecated. Please use utf8mb4 instead.

  • The following character sets are deprecated:

    In MySQL 8.0.28 and later, any of these character sets or their collations produces a deprecation warning when used in either of the following ways:

    You should use utf8mb4 instead any of the character sets listed previously.

    User-defined collations are deprecated. Beginning with MySQL 8.0.33, either of the following causes a warning to be written to the log:

    You should expect support for user-defined collations to be removed in a future version of MySQL.

  • Because caching_sha2_password is the default authentication plugin in MySQL 8.0 and provides a superset of the capabilities of the sha256_password authentication plugin, sha256_password is deprecated; expect it to be removed in a future version of MySQL. MySQL accounts that authenticate using sha256_password should be migrated to use caching_sha2_password instead.

  • The validate_password plugin has been reimplemented to use the component infrastructure. The plugin form of validate_password is still available but is now deprecated; expect it to be removed in a future version of MySQL. MySQL installations that use the plugin should make the transition to using the component instead. See Section, “Transitioning to the Password Validation Component”.

  • The ENGINE clause for the ALTER TABLESPACE and DROP TABLESPACE statements is deprecated.

  • The PAD_CHAR_TO_FULL_LENGTH SQL mode is deprecated.

  • AUTO_INCREMENT support is deprecated for columns of type FLOAT and DOUBLE (and any synonyms). Consider removing the AUTO_INCREMENT attribute from such columns, or convert them to an integer type.

  • The UNSIGNED attribute is deprecated for columns of type FLOAT, DOUBLE, and DECIMAL (and any synonyms). Consider using a simple CHECK constraint instead for such columns.

  • FLOAT(M,D) and DOUBLE(M,D) syntax to specify the number of digits for columns of type FLOAT and DOUBLE (and any synonyms) is a nonstandard MySQL extension. This syntax is deprecated.

  • The ZEROFILL attribute is deprecated for numeric data types, as is the display width attribute for integer data types. Consider using an alternative means of producing the effect of these attributes. For example, applications could use the LPAD() function to zero-pad numbers up to the desired width, or they could store the formatted numbers in CHAR columns.

  • For string data types, the BINARY attribute is a nonstandard MySQL extension that is shorthand for specifying the binary (_bin) collation of the column character set (or of the table default character set if no column character set is specified). In MySQL 8.0, this nonstandard use of BINARY is ambiguous because the utf8mb4 character set has multiple _bin collations, so the BINARY attribute is deprecated; expect support for it to be removed in a future version of MySQL. Applications should be adjusted to use an explicit _bin collation instead.

    The use of BINARY to specify a data type or character set remains unchanged.

  • Previous versions of MySQL supported the nonstandard shorthand expressions ASCII and UNICODE, respectively, for CHARACTER SET latin1 and CHARACTER SET ucs2. ASCII and UNICODE are deprecated (MySQL 8.0.28 and later) and now produce a warning. Use CHARACTER SET instead, in both cases.

  • The nonstandard C-style &&, ||, and ! operators that are synonyms for the standard SQL AND, OR, and NOT operators, respectively, are deprecated. Applications that use the nonstandard operators should be adjusted to use the standard operators.


    Use of || is deprecated unless the PIPES_AS_CONCAT SQL mode is enabled. In that case, || signifies the SQL-standard string concatenation operator).

  • The JSON_MERGE() function is deprecated. Use JSON_MERGE_PRESERVE() instead.

  • The SQL_CALC_FOUND_ROWS query modifier and accompanying FOUND_ROWS() function are deprecated. See the FOUND_ROWS() description for information about an alternative strategy.

  • Support for TABLESPACE = innodb_file_per_table and TABLESPACE = innodb_temporary clauses with CREATE TEMPORARY TABLE is deprecated as of MySQL 8.0.13.

  • For SELECT statements, use of an INTO clause after FROM but not at the end of the SELECT is deprecated as of MySQL 8.0.20. It is preferred to place the INTO at the end of the statement.

    For UNION statements, these two variants containing INTO are deprecated as of MySQL 8.0.20:

    • In the trailing query block of a query expression, use of INTO before FROM.

    • In a parenthesized trailing block of a query expression, use of INTO, regardless of its position relative to FROM.

    See Section, “SELECT ... INTO Statement”, and Section 15.2.18, “UNION Clause”.

  • FLUSH HOSTS is deprecated as of MySQL 8.0.23. Instead, truncate the Performance Schema host_cache table:

    TRUNCATE TABLE performance_schema.host_cache;

    The TRUNCATE TABLE operation requires the DROP privilege for the table.

  • The mysql_upgrade client is deprecated because its capabilities for upgrading the system tables in the mysql system schema and objects in other schemas have been moved into the MySQL server. See Section 3.4, “What the MySQL Upgrade Process Upgrades”.

  • The --no-dd-upgrade server option is deprecated. It is superseded by the --upgrade option, which provides finer control over data dictionary and server upgrade behavior.

  • The mysql_upgrade_info file, which is created data directory and used to store the MySQL version number, is deprecated; expect it to be removed in a future version of MySQL.

  • The relay_log_info_file system variable and --master-info-file option are deprecated. Previously, these were used to specify the name of the relay log info log and source info log when relay_log_info_repository=FILE and master_info_repository=FILE were set, but those settings have been deprecated. The use of files for the relay log info log and source info log has been superseded by crash-safe replica tables, which are the default in MySQL 8.0.

  • The max_length_for_sort_data system variable is now deprecated due to optimizer changes that make it obsolete and of no effect.

  • These legacy parameters for compression of connections to the server are deprecated: The --compress client command-line option; the MYSQL_OPT_COMPRESS option for the mysql_options() C API function; the slave_compressed_protocol system variable. For information about parameters to use instead, see Section 6.2.8, “Connection Compression Control”.

  • Use of the MYSQL_PWD environment variable to specify a MySQL password is deprecated.

  • Use of VALUES() to access new row values in INSERT ... ON DUPLICATE KEY UPDATE is deprecated as of MySQL 8.0.20. Use aliases for the new row and columns, instead.

  • Because specifying ON ERROR before ON EMPTY when invoking JSON_TABLE() is counter to the SQL standard, this syntax is now deprecated in MySQL. Beginning with MySQL 8.0.20, the server prints a warning whenever you attempt to do so. When specifying both of these clauses in a single JSON_TABLE() invocation, make sure that ON EMPTY is used first.

  • Columns with index prefixes have never been supported as part of a table's partitioning key; previously, these were allowed when creating, altering, or upgrading partitioned tables but were excluded by the table's partitioning function, and no warning that this had occurred was issued by the server. This permissive behavior is now deprecated, and subject to removal in a future version of MySQL in which using any such columns in the partitioning key causes the CREATE TABLE or ALTER TABLE statement in they occur to be rejected.

    As of MySQL 8.0.21, whenever columns using index prefixes are specified as part of the partitioning key, a warning is generated for each such column. Whenever a CREATE TABLE or ALTER TABLE statement is rejected because all columns in the proposed partitioning key would have index prefixes, the resulting error now provides the exact reason for the rejection. In either instance, this includes cases in which the columns used in the partitioning function are defined implicitly as those in the table's primary key by employing an empty PARTITION BY KEY() clause.

    For more information and examples, see Column index prefixes not supported for key partitioning.

  • The InnoDB memcached plugin is deprecated as of MySQL 8.0.22; expect support for it to be removed in a future version of MySQL.

  • The temptable_use_mmap variable is deprecated as of MySQL 8.0.26; expect support for it to be removed in a future version of MySQL.

  • The BINARY operator is deprecated as of MySQL 8.0.27, and you should expect its removal in a future version of MySQL. Use of BINARY now causes a warning. Use CAST(... AS BINARY) instead.

  • The default_authentication_plugin variable is deprecated as of MySQL 8.0.27; expect support for it to be removed in a future version of MySQL.

    The default_authentication_plugin variable is still used in MySQL 8.0.27, but in conjunction with and at a lower precedence than the new authentication_policy system variable, which is introduced in MySQL 8.0.27 with the multifactor authentication feature. For details, see The Default Authentication Plugin.

  • The --abort-slave-event-count and --disconnect-slave-event-count server options, used by the MySQL test suite and not normally used in production, are deprecated as of MySQL 8.0.29; expect both options to be removed in a future version of MySQL.

  • The myisam_repair_threads system variable and myisamchk --parallel-recover option are deprecated as of MySQL 8.0.29; expect support for both to be removed in a future release of MySQL.

    From MySQL 8.0.29, values other than 1 (the default) for myisam_repair_threads produce a warning.

  • Previously, MySQL accepted DATE, TIME, DATETIME, and TIMESTAMP literals containing an arbitrary number of (arbitrary) delimiter characters, as well as DATETIME and TIMESTAMP literals with an arbitrary number of whitespace characters before, after, and between the date and time parts. As of MySQL 8.0.29, the server raises a deprecation warning whenever the literal value contains any of the following:

    • One or more nonstandard delimiter characters

    • Excess delimiter characters

    • Whitespace other than the space character (' ', 0x20)

    • Excess space characters

    One deprecation warning is issued per temporal value, even if there are multiple issues with it. This warning is not promoted to an error in strict mode, so that performing an INSERT of such a value still succeeds when strict mode is in effect.

    You should expect the nonstandard behavior to be removed in a future version of MySQL, and take steps now to insure that your applications do not depend on it.

    See String and Numeric Literals in Date and Time Context, for more information and examples.

  • The replica_parallel_type system variable and its associated server option --replica-parallel-type are deprecated as of MySQL 8.0.29. Beginning with this release, reading or setting this value raises a deprecation warning; expect it to be removed in a future version of MySQL.

  • Beginning with MySQL 8.0.30, setting the replica_parallel_workers system variable (or the equivalent server option) to 0 is deprecated, and elicits a warning. When you want a replica to use single threading, use replica_parallel_workers=1 instead, which produces the same result, but with no warning.

  • The --skip-host-cache server option is deprecated beginning with MySQL 8.0.30; expect its removal in a future MySQL release. Use the host_cache_size system variable instead.

  • The --old-style-user-limits option, intended for backwards compatibility with very old (pre-5.0.3) releases, is deprecated as of MySQL 8.0.30; using it now raises a warning. You should expect this option to be removed in a future release of MySQL.

  • The innodb_log_files_in_group and innodb_log_file_size variables are deprecated as of MySQL 8.0.30. These variables are superseded by the innodb_redo_log_capacity variable. For more information, see Section 17.6.5, “Redo Log”.

  • As of MySQL 8.0.32, the use of FULL as an unquoted identifier is deprecated, due to the fact that it is a reserved keyword in the SQL standard. This means that a statement such as CREATE TABLE full (c1 INT, c2 INT) now raises a warning (ER_WARN_DEPRECATED_TO_BE_REMOVED_IDENT_FULL). To prevent this from happening, change the name or, as shown here, encase it in backticks (`):

    CREATE TABLE `full` (c1 INT, c2 INT);

    For more information, see Section 11.3, “Keywords and Reserved Words”.

  • Beginning with MySQL 8.0.32, the use of the dollar sign ($) as the leading character of an unquoted identifier is deprecated and produces a warning. Such usage is subject to removal in a future release of MySQL. This includes identifiers used as names of databases, tables, views, columns, or stored programs, as well as aliases for any of these. The dollar sign may still be used as the first character of a quoted identifier. See Section 11.2, “Schema Object Names”, for more information.

  • The binlog_format server system variable is deprecated as of MySQL 8.0.34, and is subject to being removed in a future release. Changing the binary logging format, is also deprecated, with the expectation that the removal of binlog_format will leave row-based binary logging, already the default in MySQL 8.0, as the only binary logging format used or supported by MySQL. For this reason, new MySQL installations should use only row-based binary logging; existing replication setups using binlog_format=STATEMENT or binlog_format=MIXED logging format should be migrated to the row-based format.

    The system variables log_bin_trust_function_creators and log_statements_unsafe_for_binlog, are used exclusively for statement-based logging and replication. For this reason, they are now also deprecated, and subject to removal in a future version of MySQL.

    Setting or selecting the value of binlog_format, log_bin_trust_function_creators, or log_statements_unsafe_for_binlog raises a warning in MySQL 8.0.34 and later.

  • The mysqlpump client utility program is deprecated beginning with MySQL 8.0.34, and produces a deprecation warning when invoked. This program is subject to removal in a future version of MySQL. Since MySQL provides other means of performing database dumps and backups with the same or additional functionality, including mysqldump and MySQL Shell, this program is now considered redundant.

    The associated lz4_decompress and zlib_decompress utilities are also deprecated as of MySQL 8.0.34.

  • The use of a version number without a whitespace character following (or end of comment) is deprecated as of MySQL 8.0.34, and raises a warning. This statement raises a warning in MySQL 8.0.34 or later, as shown here:

    mysql> CREATE TABLE t1(a INT, KEY (a)) /*!50110KEY_BLOCK_SIZE=1024*/ ENGINE=MYISAM;
    Query OK, 0 rows affected, 1 warning (0.01 sec)
    mysql> SHOW WARNINGS\G
    *************************** 1. row ***************************
      Level: Warning
       Code: 4164
    Message: Immediately starting the version comment after the version number is
    deprecated and may change behavior in a future release. Please insert a
    white-space character after the version number.  
    1 row in set (0.00 sec)

    To avoid such warnings, insert one or more whitespace characters after the version number, like this:

    mysql> CREATE TABLE t2(a INT, KEY (a)) /*!50110 KEY_BLOCK_SIZE=1024*/ ENGINE=MYISAM;
    Query OK, 0 rows affected (0.00 sec)

    See also Section 11.7, “Comments”.

  • As of MySQL 8.0.34, the sync_relay_log_info system variable is deprecated, along with its equivalent server startup option --sync-relay-log-info. You should expect support for this variable, and for storing replication applier metadata in a file, to be removed in a future version of MySQL. You are advised to update any of your MySQL applications which may depend on it before this occurs.

  • The binlog_transaction_dependency_tracking server system variable is deprecated as of MySQL 8.0.35, and subject to removal in a future version of MySQL. Referencing this variable or the equivalent mysqld startup option --binlog-transaction-dependency-tracking now triggers a warning. There are no plans to replace this variable or its functionality, which is expected later to be made internal to the server.

Features Removed in MySQL 8.0

The following items are obsolete and have been removed in MySQL 8.0. Where alternatives are shown, applications should be updated to use them.

For MySQL 5.7 applications that use features removed in MySQL 8.0, statements may fail when replicated from a MySQL 5.7 source to a MySQL 8.0 replica, or may have different effects on source and replica. To avoid such problems, applications that use features removed in MySQL 8.0 should be revised to avoid them and use alternatives when possible.

  • The innodb_locks_unsafe_for_binlog system variable was removed. The READ COMMITTED isolation level provides similar functionality.

  • The information_schema_stats variable, introduced in MySQL 8.0.0, was removed and replaced by information_schema_stats_expiry in MySQL 8.0.3.

    information_schema_stats_expiry defines an expiration setting for cached INFORMATION_SCHEMA table statistics. For more information, see Section 10.2.3, “Optimizing INFORMATION_SCHEMA Queries”.

  • Code related to obsolete InnoDB system tables was removed in MySQL 8.0.3. INFORMATION_SCHEMA views based on InnoDB system tables were replaced by internal system views on data dictionary tables. Affected InnoDB INFORMATION_SCHEMA views were renamed:

    Table 1.1 Renamed InnoDB Information Schema Views

    Old Name New Name

    After upgrading to MySQL 8.0.3 or later, update any scripts that reference previous InnoDB INFORMATION_SCHEMA view names.

  • The following features related to account management are removed:

    • Using GRANT to create users. Instead, use CREATE USER. Following this practice makes the NO_AUTO_CREATE_USER SQL mode immaterial for GRANT statements, so it too is removed, and an error now is written to the server log when the presence of this value for the sql_mode option in the options file prevents mysqld from starting.

    • Using GRANT to modify account properties other than privilege assignments. This includes authentication, SSL, and resource-limit properties. Instead, establish such properties at account-creation time with CREATE USER or modify them afterward with ALTER USER.

    • IDENTIFIED BY PASSWORD 'auth_string' syntax for CREATE USER and GRANT. Instead, use IDENTIFIED WITH auth_plugin AS 'auth_string' for CREATE USER and ALTER USER, where the 'auth_string' value is in a format compatible with the named plugin.

      Additionally, because IDENTIFIED BY PASSWORD syntax was removed, the log_builtin_as_identified_by_password system variable is superfluous and was removed.

    • The PASSWORD() function. Additionally, PASSWORD() removal means that SET PASSWORD ... = PASSWORD('auth_string') syntax is no longer available.

    • The old_passwords system variable.

  • The query cache was removed. Removal includes these items:


    • These system variables: query_cache_limit, query_cache_min_res_unit, query_cache_size, query_cache_type, query_cache_wlock_invalidate.

    • These status variables: Qcache_free_blocks, Qcache_free_memory, Qcache_hits, Qcache_inserts, Qcache_lowmem_prunes, Qcache_not_cached, Qcache_queries_in_cache, Qcache_total_blocks.

    • These thread states: checking privileges on cached query, checking query cache for query, invalidating query cache entries, sending cached result to client, storing result in query cache, Waiting for query cache lock.

    • The SQL_CACHE SELECT modifier.

    These deprecated query cache items remain deprecated, but have no effect; expect them to be removed in a future MySQL release:

    • The SQL_NO_CACHE SELECT modifier.

    • The ndb_cache_check_time system variable.

    The have_query_cache system variable remains deprecated, and always has a value of NO; expect it to be removed in a future MySQL release.

  • The data dictionary provides information about database objects, so the server no longer checks directory names in the data directory to find databases. Consequently, the --ignore-db-dir option and ignore_db_dirs system variables are extraneous and are removed.

  • The DDL log, also known as the metadata log, has been removed. Beginning with MySQL 8.0.3, this functionality is handled by the data dictionary innodb_ddl_log table. See Viewing DDL Logs.

  • The tx_isolation and tx_read_only system variables have been removed. Use transaction_isolation and transaction_read_only instead.

  • The sync_frm system variable has been removed because .frm files have become obsolete.

  • The secure_auth system variable and --secure-auth client option have been removed. The MYSQL_SECURE_AUTH option for the mysql_options() C API function was removed.

  • The multi_range_count system variable is removed.

  • The log_warnings system variable and --log-warnings server option have been removed. Use the log_error_verbosity system variable instead.

  • The global scope for the sql_log_bin system variable was removed. sql_log_bin has session scope only, and applications that rely on accessing @@GLOBAL.sql_log_bin should be adjusted.

  • The metadata_locks_cache_size and metadata_locks_hash_instances system variables are removed.

  • The unused date_format, datetime_format, time_format, and max_tmp_tables system variables are removed.

  • These deprecated compatibility SQL modes are removed: DB2, MAXDB, MSSQL, MYSQL323, MYSQL40, ORACLE, POSTGRESQL, NO_FIELD_OPTIONS, NO_KEY_OPTIONS, NO_TABLE_OPTIONS. They can no longer be assigned to the sql_mode system variable or used as permitted values for the mysqldump --compatible option.

    Removal of MAXDB means that the TIMESTAMP data type for CREATE TABLE or ALTER TABLE is treated as TIMESTAMP, and is no longer treated as DATETIME.

  • The deprecated ASC or DESC qualifiers for GROUP BY clauses are removed. Queries that previously relied on GROUP BY sorting may produce results that differ from previous MySQL versions. To produce a given sort order, provide an ORDER BY clause.

  • The EXTENDED and PARTITIONS keywords for the EXPLAIN statement have been removed. These keywords are unnecessary because their effect is always enabled.

  • These encryption-related items are removed:

    • The ENCODE() and DECODE() functions.

    • The ENCRYPT() function.

    • The DES_ENCRYPT(), and DES_DECRYPT() functions, the --des-key-file option, the have_crypt system variable, the DES_KEY_FILE option for the FLUSH statement, and the HAVE_CRYPT CMake option.

    In place of the removed encryption functions: For ENCRYPT(), consider using SHA2() instead for one-way hashing. For the others, consider using AES_ENCRYPT() and AES_DECRYPT() instead.

  • In MySQL 5.7, several spatial functions available under multiple names were deprecated to move in the direction of making the spatial function namespace more consistent, the goal being that each spatial function name begin with ST_ if it performs an exact operation, or with MBR if it performs an operation based on minimum bounding rectangles. In MySQL 8.0, the deprecated functions are removed to leave only the corresponding ST_ and MBR functions:

    • These functions are removed in favor of the MBR names: Contains(), Disjoint(), Equals(), Intersects(), Overlaps(), Within().

    • These functions are removed in favor of the ST_ names: Area(), AsBinary(), AsText(), AsWKB(), AsWKT(), Buffer(), Centroid(), ConvexHull(), Crosses(), Dimension(), Distance(), EndPoint(), Envelope(), ExteriorRing(), GeomCollFromText(), GeomCollFromWKB(), GeomFromText(), GeomFromWKB(), GeometryCollectionFromText(), GeometryCollectionFromWKB(), GeometryFromText(), GeometryFromWKB(), GeometryN(), GeometryType(), InteriorRingN(), IsClosed(), IsEmpty(), IsSimple(), LineFromText(), LineFromWKB(), LineStringFromText(), LineStringFromWKB(), MLineFromText(), MLineFromWKB(), MPointFromText(), MPointFromWKB(), MPolyFromText(), MPolyFromWKB(), MultiLineStringFromText(), MultiLineStringFromWKB(), MultiPointFromText(), MultiPointFromWKB(), MultiPolygonFromText(), MultiPolygonFromWKB(), NumGeometries(), NumInteriorRings(), NumPoints(), PointFromText(), PointFromWKB(), PointN(), PolyFromText(), PolyFromWKB(), PolygonFromText(), PolygonFromWKB(), SRID(), StartPoint(), Touches(), X(), Y().

    • GLength() is removed in favor of ST_Length().

  • The functions described in Section 14.16.4, “Functions That Create Geometry Values from WKB Values” previously accepted either WKB strings or geometry arguments. Geometry arguments are no longer permitted and produce an error. See that section for guidelines for migrating queries away from using geometry arguments.

  • The parser no longer treats \N as a synonym for NULL in SQL statements. Use NULL instead.

    This change does not affect text file import or export operations performed with LOAD DATA or SELECT ... INTO OUTFILE, for which NULL continues to be represented by \N. See Section 15.2.9, “LOAD DATA Statement”.

  • PROCEDURE ANALYSE() syntax is removed.

  • The client-side --ssl and --ssl-verify-server-cert options have been removed. Use --ssl-mode=REQUIRED instead of --ssl=1 or --enable-ssl. Use --ssl-mode=DISABLED instead of --ssl=0, --skip-ssl, or --disable-ssl. Use --ssl-mode=VERIFY_IDENTITY instead of --ssl-verify-server-cert options. (The server-side --ssl option is still available, but is deprecated as of MySQL 8.0.26 and subject to removal in a future MySQL version.)

    For the C API, MYSQL_OPT_SSL_ENFORCE and MYSQL_OPT_SSL_VERIFY_SERVER_CERT options for mysql_options() correspond to the client-side --ssl and --ssl-verify-server-cert options and are removed. Use MYSQL_OPT_SSL_MODE with an option value of SSL_MODE_REQUIRED or SSL_MODE_VERIFY_IDENTITY instead.

  • The --temp-pool server option was removed.

  • The ignore_builtin_innodb system variable is removed.

  • The server no longer performs conversion of pre-MySQL 5.1 database names containing special characters to 5.1 format with the addition of a #mysql50# prefix. Because these conversions are no longer performed, the --fix-db-names and --fix-table-names options for mysqlcheck, the UPGRADE DATA DIRECTORY NAME clause for the ALTER DATABASE statement, and the Com_alter_db_upgrade status variable are removed.

    Upgrades are supported only from one major version to another (for example, 5.0 to 5.1, or 5.1 to 5.5), so there should be little remaining need for conversion of older 5.0 database names to current versions of MySQL. As a workaround, upgrade a MySQL 5.0 installation to MySQL 5.1 before upgrading to a more recent release.

  • The mysql_install_db program has been removed from MySQL distributions. Data directory initialization should be performed by invoking mysqld with the --initialize or --initialize-insecure option instead. In addition, the --bootstrap option for mysqld that was used by mysql_install_db was removed, and the INSTALL_SCRIPTDIR CMake option that controlled the installation location for mysql_install_db was removed.

  • The generic partitioning handler was removed from the MySQL server. In order to support partitioning of a given table, the storage engine used for the table must now provide its own (native) partitioning handler. The --partition and --skip-partition options are removed from the MySQL Server, and partitioning-related entries are no longer shown in the output of SHOW PLUGINS or in the Information Schema PLUGINS table.

    Two MySQL storage engines currently provide native partitioning support: InnoDB and NDB. Of these, only InnoDB is supported in MySQL 8.0. Any attempt to create partitioned tables in MySQL 8.0 using any other storage engine fails.

    Ramifications for upgrades.  The direct upgrade of a partitioned table using a storage engine other than InnoDB (such as MyISAM) from MySQL 5.7 (or earlier) to MySQL 8.0 is not supported. There are two options for handling such a table:

    At least one of the two operations just listed must be performed for each partitioned non-InnoDB table prior to upgrading the server to MySQL 8.0. Otherwise, such a table cannot be used following the upgrade.

    Due to the fact that table creation statements that would result in a partitioned table using a storage engine without partitioning support now fail with an error (ER_CHECK_NOT_IMPLEMENTED), you must make sure that any statements in a dump file (such as that written by mysqldump) from an older version of MySQL that you wish to import into a MySQL 8.0 server that create partitioned tables do not also specify a storage engine such as MyISAM that has no native partitioning handler. You can do this by performing either of the following:

    • Remove any references to partitioning from CREATE TABLE statements that use a value for the STORAGE ENGINE option other than InnoDB.

    • Specifying the storage engine as InnoDB, or allow InnoDB to be used as the table's storage engine by default.

    For more information, see Section 26.6.2, “Partitioning Limitations Relating to Storage Engines”.

  • System and status variable information is no longer maintained in the INFORMATION_SCHEMA. These tables are removed: GLOBAL_VARIABLES, SESSION_VARIABLES, GLOBAL_STATUS, SESSION_STATUS. Use the corresponding Performance Schema tables instead. See Section 29.12.14, “Performance Schema System Variable Tables”, and Section 29.12.15, “Performance Schema Status Variable Tables”. In addition, the show_compatibility_56 system variable was removed. It was used in the transition period during which system and status variable information in INFORMATION_SCHEMA tables was moved to Performance Schema tables, and is no longer needed. These status variables are removed: Slave_heartbeat_period, Slave_last_heartbeat, Slave_received_heartbeats, Slave_retried_transactions, Slave_running. The information they provided is available in Performance Schema tables; see Migrating to Performance Schema System and Status Variable Tables.

  • The Performance Schema setup_timers table was removed, as was the TICK row in the performance_timers table.

  • The libmysqld embedded server library is removed, along with:


    • The mysql_config --libmysqld-libs, --embedded-libs, and --embedded options


    • The (undocumented) mysql --server-arg option

    • The mysqltest --embedded-server, --server-arg, and --server-file options

    • The mysqltest_embedded and mysql_client_test_embedded test programs

  • The mysql_plugin utility was removed. Alternatives include loading plugins at server startup using the --plugin-load or --plugin-load-add option, or at runtime using the INSTALL PLUGIN statement.

  • The resolveip utility is removed. nslookup, host, or dig can be used instead.

  • The resolve_stack_dump utility is removed. Stack traces from official MySQL builds are always symbolized, so there is no need to use resolve_stack_dump.

  • The following server error codes are not used and have been removed. Applications that test specifically for any of these errors should be updated.

  • The deprecated INFORMATION_SCHEMA INNODB_LOCKS and INNODB_LOCK_WAITS tables are removed. Use the Performance Schema data_locks and data_lock_waits tables instead.


    In MySQL 5.7, the LOCK_TABLE column in the INNODB_LOCKS table and the locked_table column in the sys schema innodb_lock_waits and x$innodb_lock_waits views contain combined schema/table name values. In MySQL 8.0, the data_locks table and the sys schema views contain separate schema name and table name columns. See Section, “The innodb_lock_waits and x$innodb_lock_waits Views”.

  • InnoDB no longer supports compressed temporary tables. When innodb_strict_mode is enabled (the default), CREATE TEMPORARY TABLE returns an error if ROW_FORMAT=COMPRESSED or KEY_BLOCK_SIZE is specified. If innodb_strict_mode is disabled, warnings are issued and the temporary table is created using a non-compressed row format.

  • InnoDB no longer creates .isl files (InnoDB Symbolic Link files) when creating tablespace data files outside of the MySQL data directory. The innodb_directories option now supports locating tablespace files created outside of the data directory.

    With this change, moving a remote tablespace while the server is offline by manually modifying an .isl file is no longer supported. Moving remote tablespace files is now supported by the innodb_directories option. See Section, “Moving Tablespace Files While the Server is Offline”.

  • The following InnoDB file format variables were removed:

    • innodb_file_format

    • innodb_file_format_check

    • innodb_file_format_max

    • innodb_large_prefix

    File format variables were necessary for creating tables compatible with earlier versions of InnoDB in MySQL 5.1. Now that MySQL 5.1 has reached the end of its product lifecycle, these options are no longer required.

    The FILE_FORMAT column was removed from the INNODB_TABLES and INNODB_TABLESPACES Information Schema tables.

  • The innodb_support_xa system variable, which enables support for two-phase commit in XA transactions, was removed. InnoDB support for two-phase commit in XA transactions is always enabled.

  • Support for DTrace was removed.

  • The JSON_APPEND() function was removed. Use JSON_ARRAY_APPEND() instead.

  • Support for placing table partitions in shared InnoDB tablespaces was removed in MySQL 8.0.13. Shared tablespaces include the InnoDB system tablespace and general tablespaces. For information about identifying partitions in shared tablespaces and moving them to file-per-table tablespaces, see Section 3.6, “Preparing Your Installation for Upgrade”.

  • Support for setting user variables in statements other than SET was deprecated in MySQL 8.0.13. This functionality is subject to removal in MySQL 8.4.

  • The --ndb perror option was removed. Use the ndb_perror utility instead.

  • The innodb_undo_logs variable was removed. The innodb_rollback_segments variables performs the same function and should be used instead.

  • The Innodb_available_undo_logs status variable was removed. The number of available rollback segments per tablespace may be retrieved using SHOW VARIABLES LIKE 'innodb_rollback_segments';

  • As of MySQL 8.0.14, the previously deprecated innodb_undo_tablespaces variable is no longer configurable. For more information, see Section, “Undo Tablespaces”.

  • Support for the ALTER TABLE ... UPGRADE PARTITIONING statement has been removed.

  • As of MySQL 8.0.16, support for the internal_tmp_disk_storage_engine system variable has been removed; internal temporary tables on disk now always use the InnoDB storage engine. See Storage Engine for On-Disk Internal Temporary Tables,for more information.

  • The DISABLE_SHARED CMake option was unused and has been removed.

  • The myisam_repair_threads system variable is removed as of MySQL 8.0.30.