MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0
When innodb_dedicated_server is
enabled, InnoDB automatically configures the
following variables:
innodb_log_files_in_group (as
of MySQL 8.0.14)
Only consider enabling
innodb_dedicated_server if the
MySQL instance resides on a dedicated server where it can use all
available system resources. For example, consider enabling if you
run MySQL Server in a Docker container or dedicated VM that only
runs MySQL. Enabling
innodb_dedicated_server is not
recommended if the MySQL instance shares system resources with
other applications.
The information that follows describes how each variable is automatically configured.
Buffer pool size is configured according to the amount of memory detected on the server.
Table 15.8 Automatically Configured Buffer Pool Size
| Detected Server Memory | Buffer Pool Size |
|---|---|
| Less than 1GB | 128MiB (the default value) |
| 1GB to 4GB | detected server memory * 0.5 |
| Greater than 4GB | detected server memory * 0.75 |
As of MySQL 8.0.14, log file size is configured according to the automatically configured buffer pool size.
Table 15.9 Automatically Configured Log File Size
| Buffer Pool Size | Log File Size |
|---|---|
| Less than 8GB | 512MiB |
| 8GB to 128GB | 1024MiB |
| Greater than 128GB | 2048MiB |
Prior to MySQL 8.0.14, the
innodb_log_file_size
variable was automatically configured according to the
amount of memory detected on the server, as shown below:
Table 15.10 Automatically Configured Log File Size (MySQL 8.0.13 and Earlier)
| Detected Server Memory | Log File Size |
|---|---|
| < 1GB | 48MiB (the default value) |
| <= 4GB | 128MiB |
| <= 8GB | 512MiB |
| <= 16GB | 1024MiB |
| > 16GB | 2048MiB |
The number of log files is configured according to the
automatically configured buffer pool size (in gigabytes).
Automatic configuration of the
innodb_log_files_in_group
variable was added in MySQL 8.0.14.
Table 15.11 Automatically Configured Number of Log Files
| Buffer Pool Size | Number of Log Files |
|---|---|
| Less than 8GB | ROUND(buffer pool size) |
| 8GB to 128GB | ROUND(buffer pool size * 0.75) |
| Greater than 128GB | 64 |
The minimum
innodb_log_files_in_group
value of 2 is enforced if the rounded buffer pool size value
is less than 2GB.
The flush method is set to
O_DIRECT_NO_FSYNC when
innodb_dedicated_server is
enabled. If the O_DIRECT_NO_FSYNC setting
is not available, the default
innodb_flush_method setting
is used.
InnoDB uses O_DIRECT
during flushing I/O, but skips the fsync()
system call after each write operation.
Prior to MySQL 8.0.14, this setting is not suitable for file
systems such as XFS and EXT4, which require an
fsync() system call to synchronize file
system metadata changes.
As of MySQL 8.0.14, fsync() is called
after creating a new file, after increasing file size, and
after closing a file, to ensure that file system metadata
changes are synchronized. The fsync()
system call is still skipped after each write operation.
Data loss is possible if redo log files and data files
reside on different storage devices, and an unexpected exit
occurs before data file writes are flushed from a device
cache that is not battery-backed. If you use or intend to
use different storage devices for redo log files and data
files, and your data files reside on a device with a cache
that is not battery-backed, use O_DIRECT
instead.
If an automatically configured option is configured explicitly in
an option file or elsewhere, the explicitly specified setting is
used, and a startup warning similar to this is printed to
stderr:
[Warning] [000000] InnoDB: Option innodb_dedicated_server is ignored for innodb_buffer_pool_size because innodb_buffer_pool_size=134217728 is specified explicitly.
Explicit configuration of one option does not prevent the automatic configuration of other options.
If innodb_dedicated_server is
enabled and
innodb_buffer_pool_size is
configured explicitly in an option file,
innodb_log_file_size and
innodb_log_files_in_group are
still automatically configured based on a buffer pool size value
calculated according to the amount of memory detected on the
server, even though that value is not used to configure the size
of the buffer pool.
Automatically configured settings are evaluated and reconfigured if necessary each time the MySQL server is started.