MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0
This section describes the system variables that control operation of the clone plugin. If values specified at startup are incorrect, the clone plugin may fail to initialize properly and the server does not load it. In this case, the server may also produce error messages for other clone settings because it does not recognize them.
Each system variable has a default value. System variables can
be set at server startup using options on the command line or in
an option file. They can be changed dynamically at runtime using
the SET statement, which enables
you to modify operation of the server without having to stop and
restart it.
Setting a global system variable runtime value normally requires
the SYSTEM_VARIABLES_ADMIN
privilege (or the deprecated
SUPER privilege). For more
information, see Section 7.1.9.1, “System Variable Privileges”.
Clone variables are configured on the recipient MySQL server instance where the cloning operation is executed.
| Command-Line Format | --clone-autotune-concurrency |
|---|---|
| Introduced | 8.0.17 |
| System Variable | clone_autotune_concurrency |
| Scope | Global |
| Dynamic | Yes |
SET_VAR Hint Applies |
No |
| Type | Boolean |
| Default Value | ON |
When
clone_autotune_concurrency
is enabled (the default), additional threads for remote
cloning operations are spawned dynamically to optimize data
transfer speed. The setting is applicable to recipient MySQL
server instance only.
During a cloning operation, the number of threads increases incrementally toward a target of double the current thread count. The effect on the data transfer speed is evaluated at each increment. The process either continues or stops according to the following rules:
If the data transfer speed degrades more than 5% with an incremental increase, the process stops.
If there is at least a 5% improvement after reaching 25% of the target, the process continues. Otherwise, the process stops.
If there is at least a 10% improvement after reaching 50% of the target, the process continues. Otherwise, the process stops.
If there is at least a 25% improvement after reaching the target, the process continues toward a new target of double the current thread count. Otherwise, the process stops.
The autotuning process does not support decreasing the number of threads.
The clone_max_concurrency
variable defines the maximum number of threads that can be
spawned.
If
clone_autotune_concurrency
is disabled,
clone_max_concurrency
defines the number of threads spawned for a remote cloning
operation.
| Command-Line Format | --clone-buffer-size |
|---|---|
| Introduced | 8.0.17 |
| System Variable | clone_buffer_size |
| Scope | Global |
| Dynamic | Yes |
SET_VAR Hint Applies |
No |
| Type | Integer |
| Default Value | 4194304 |
| Minimum Value | 1048576 |
| Maximum Value | 268435456 |
| Unit | bytes |
Defines the size of the intermediate buffer used when transferring data during a local cloning operation. The default value is 4 mebibytes (MiB). A larger buffer size may permit I/O device drivers to fetch data in parallel, which can improve cloning performance.
| Command-Line Format | --clone-block-ddl |
|---|---|
| Introduced | 8.0.27 |
| System Variable | clone_block_ddl |
| Scope | Global |
| Dynamic | Yes |
SET_VAR Hint Applies |
No |
| Type | Boolean |
| Default Value | OFF |
Enables an exclusive backup lock on the donor MySQL Server instance during a cloning operation, which blocks concurrent DDL operations on the donor. See Section 7.6.7.4, “Cloning and Concurrent DDL”.
| Command-Line Format | --clone-delay-after-data-drop |
|---|---|
| Introduced | 8.0.29 |
| System Variable | clone_delay_after_data_drop |
| Scope | Global |
| Dynamic | Yes |
SET_VAR Hint Applies |
No |
| Type | Integer |
| Default Value | 0 |
| Minimum Value | 0 |
| Maximum Value | 3600 |
| Unit | bytes |
Specifies 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 such as VxFS 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).
This variable is applicable to remote cloning operation only and is configured on the recipient MySQL Server instance.
| Command-Line Format | --clone-ddl-timeout |
|---|---|
| Introduced | 8.0.17 |
| System Variable | clone_ddl_timeout |
| Scope | Global |
| Dynamic | Yes |
SET_VAR Hint Applies |
No |
| Type | Integer |
| Default Value | 300 |
| Minimum Value | 0 |
| Maximum Value | 2592000 |
| Unit | seconds |
The time in seconds that a cloning operation waits for a backup lock. The backup lock blocks concurrent DDL when executing a cloning operation. This setting is applied on both the donor and recipient MySQL server instances.
A setting of 0 means that the cloning operation does not wait for a backup lock. In this case, executing a concurrent DDL operation can cause the cloning operation to fail.
Prior to MySQL 8.0.27, the backup lock blocks concurrent DDL
operations on both the donor and recipient during a cloning
operation, and a cloning operation cannot proceed until
current DDL operations finish. As of MySQL 8.0.27,
concurrent DDL is permitted on the donor during a cloning
operation if
clone_block_ddl variable is
set to OFF (the default). In this case,
the cloning operation does not have to wait for a backup
lock on the donor. See
Section 7.6.7.4, “Cloning and Concurrent DDL”.
clone_donor_timeout_after_network_failure
| Command-Line Format | --clone-donor-timeout-after-network-failure |
|---|---|
| Introduced | 8.0.24 |
| System Variable | clone_donor_timeout_after_network_failure |
| Scope | Global |
| Dynamic | Yes |
SET_VAR Hint Applies |
No |
| Type | Integer |
| Default Value | 5 |
| Minimum Value | 0 |
| Maximum Value | 30 |
| Unit | minutes |
Defines the amount of time in minutes the donor allows for the recipient to reconnect and restart a cloning operation after a network failure. For more information, see Section 7.6.7.9, “Remote Cloning Operation Failure Handling”.
This variable is set on the donor MySQL server instance. Setting it on the recipient MySQL server instance has no effect.
| Command-Line Format | --clone-enable-compression |
|---|---|
| Introduced | 8.0.17 |
| System Variable | clone_enable_compression |
| Scope | Global |
| Dynamic | Yes |
SET_VAR Hint Applies |
No |
| Type | Boolean |
| Default Value | OFF |
Enables compression of data at the network layer during a remote cloning operation. Compression saves network bandwidth at the cost of CPU. Enabling compression may improve the data transfer rate. This setting is only applied on the recipient MySQL server instance.
| Command-Line Format | --clone-max-concurrency |
|---|---|
| Introduced | 8.0.17 |
| System Variable | clone_max_concurrency |
| Scope | Global |
| Dynamic | Yes |
SET_VAR Hint Applies |
No |
| Type | Integer |
| Default Value | 16 |
| Minimum Value | 1 |
| Maximum Value | 128 |
| Unit | threads |
Defines the maximum number of concurrent threads for a remote cloning operation. The default value is 16. A greater number of threads can improve cloning performance but also reduces the number of permitted simultaneous client connections, which can affect the performance of existing client connections. This setting is only applied on the recipient MySQL server instance.
If
clone_autotune_concurrency
is enabled (the default),
clone_max_concurrency is
the maximum number of threads that can be dynamically
spawned for a remote cloning operation. If
clone_autotune_concurrency
is disabled,
clone_max_concurrency
defines the number of threads spawned for a remote cloning
operation.
A minimum data transfer rate of 1 mebibyte (MiB) per thread
is recommended for remote cloning operations. The data
transfer rate for a remote cloning operation is controlled
by the
clone_max_data_bandwidth
variable.
| Command-Line Format | --clone-max-data-bandwidth |
|---|---|
| Introduced | 8.0.17 |
| System Variable | clone_max_data_bandwidth |
| Scope | Global |
| Dynamic | Yes |
SET_VAR Hint Applies |
No |
| Type | Integer |
| Default Value | 0 |
| Minimum Value | 0 |
| Maximum Value | 1048576 |
| Unit | miB/second |
Defines the maximum data transfer rate in mebibytes (MiB) per second for a remote cloning operation. This variable helps manage the performance impact of a cloning operation. A limit should be set only when donor disk I/O bandwidth is saturated, affecting performance. A value of 0 means “unlimited”, which permits cloning operations to run at the highest possible data transfer rate. This setting is only applicable to the recipient MySQL server instance.
The minimum data transfer rate is 1 MiB per second, per
thread. For example, if there are 8 threads, the minimum
transfer rate is 8 MiB per second. The
clone_max_concurrency
variable controls the maximum number threads spawned for a
remote cloning operation.
The requested data transfer rate specified by
clone_max_data_bandwidth
may differ from the actual data transfer rate reported by
the DATA_SPEED column in the
performance_schema.clone_progress table.
If your cloning operation is not achieving the desired data
transfer rate and you have available bandwidth, check I/O
usage on the recipient and donor. If there is underutilized
bandwidth, I/O is the next mostly likely bottleneck.
| Command-Line Format | --clone-max-network-bandwidth |
|---|---|
| Introduced | 8.0.17 |
| System Variable | clone_max_network_bandwidth |
| Scope | Global |
| Dynamic | Yes |
SET_VAR Hint Applies |
No |
| Type | Integer |
| Default Value | 0 |
| Minimum Value | 0 |
| Maximum Value | 1048576 |
| Unit | miB/second |
Specifies the maximum approximate network transfer rate in mebibytes (MiB) per second for a remote cloning operation. This variable can be used to manage the performance impact of a cloning operation on network bandwidth. It should be set only when network bandwidth is saturated, affecting performance on the donor instance. A value of 0 means “unlimited”, which permits cloning at the highest possible data transfer rate over the network, providing the best performance. This setting is only applicable to the recipient MySQL server instance.
| Command-Line Format | --clone-ssl-ca=file_name |
|---|---|
| Introduced | 8.0.14 |
| System Variable | clone_ssl_ca |
| Scope | Global |
| Dynamic | Yes |
SET_VAR Hint Applies |
No |
| Type | File name |
| Default Value | empty string |
Specifies the path to the certificate authority (CA) file. Used to configure an encrypted connection for a remote cloning operation. This setting configured on the recipient and used when connecting to the donor.
| Command-Line Format | --clone-ssl-cert=file_name |
|---|---|
| Introduced | 8.0.14 |
| System Variable | clone_ssl_cert |
| Scope | Global |
| Dynamic | Yes |
SET_VAR Hint Applies |
No |
| Type | File name |
| Default Value | empty string |
Specifies the path to the public key certificate. Used to configure an encrypted connection for a remote cloning operation. This setting configured on the recipient and used when connecting to the donor.
| Command-Line Format | --clone-ssl-key=file_name |
|---|---|
| Introduced | 8.0.14 |
| System Variable | clone_ssl_key |
| Scope | Global |
| Dynamic | Yes |
SET_VAR Hint Applies |
No |
| Type | File name |
| Default Value | empty string |
Specifies the path to the private key file. Used to configure an encrypted connection for a remote cloning operation. This setting configured on the recipient and used when connecting to the donor.
| Command-Line Format | --clone-valid-donor-list=value |
|---|---|
| Introduced | 8.0.17 |
| System Variable | clone_valid_donor_list |
| Scope | Global |
| Dynamic | Yes |
SET_VAR Hint Applies |
No |
| Type | String |
| Default Value | NULL |
Defines valid donor host addresses for remote cloning
operations. This setting is applied on the recipient MySQL
server instance. A comma-separated list of values is
permitted in the following format:
“HOST1:PORT1,HOST2:PORT2,HOST3:PORT3”.
Spaces are not permitted.
The clone_valid_donor_list
variable adds a layer of security by providing control over
the sources of cloned data. The privilege required to
configure
clone_valid_donor_list is
different from the privilege required to execute remote
cloning operations, which permits assigning those
responsibilities to different roles. Configuring
clone_valid_donor_list
requires the
SYSTEM_VARIABLES_ADMIN
privilege, whereas executing a remote cloning operation
requires the CLONE_ADMIN
privilege.
Internet Protocol version 6 (IPv6) address format is not supported. Internet Protocol version 6 (IPv6) address format is not supported. An alias to the IPv6 address can be used instead. An IPv4 address can be used as is.