17.8.12 Enabling Automatic InnoDB Configuration for a Dedicated MySQL Server

When the server is started with --innodb-dedicated-server, InnoDB automatically calculates values for and sets the following system variables:

• innodb_buffer_pool_size

• innodb_redo_log_capacity (MySQL 8.0.30 and later)

• innodb_log_file_size (prior to MySQL 8.0.30)

• innodb_log_files_in_group (prior to MySQL 8.0.30)

• innodb_flush_method

Note

innodb_log_file_size and innodb_log_files_in_group are deprecated as of MySQL 8.0.30, and are superseded by innodb_redo_log_capacity. You should expect innodb_log_file_size and innodb_log_files_in_group to be removed in a future version of MySQL.

You should consider using --innodb-dedicated-server only if the MySQL instance resides on a dedicated server where it can use all available system resources—for example, if you run MySQL Server in a Docker container or dedicated VM that runs MySQL only. using --innodb-dedicated-server is not recommended if the MySQL instance shares system resources with other applications.

The value for each affected variable is determined and applied by --innodb-dedicated-server as described in the following list:

• innodb_buffer_pool_size

  Buffer pool size is calculated according to the amount of memory detected on the server, as shown in the following table:

  Table 17.8 Automatically Configured Buffer Pool Size

  Detected Server Memory	Buffer Pool Size
  Less than 1GB	128MB (the default value)
  1GB to 4GB	detected server memory * 0.5
  Greater than 4GB	detected server memory * 0.75

  
  

• innodb_redo_log_capacity

  Redo log capacity is configured according to the amount of memory detected on the server and, in some cases, whether innodb_buffer_pool_size is configured explicitly. If innodb_buffer_pool_size is not configured explicitly, the default value is assumed.

  Warning

  Automatic redo log capacity configuration behavior is undefined if innodb_buffer_pool_size is set to a value larger than the detected amount of server memory.

  Table 17.9 Automatically Configured Log File Size

  Detected Server Memory	Buffer Pool Size	Redo Log Capacity
  Less than 1GB	Not configured	100MB
  Less than 1GB	Less than 1GB	100MB
  1GB to 2GB	Not applicable	100MB
  2GB to 4GB	Not configured	1GB
  2GB to 4GB	Any configured value	round(0.5 * detected server memory in GB) * 0.5 GB
  4GB to 10.66GB	Not applicable	round(0.75 * detected server memory in GB) * 0.5 GB
  10.66GB to 170.66GB	Not applicable	round(0.5625 * detected server memory in GB) * 1 GB
  Greater than 170.66GB	Not applicable	128GB

  
  

• innodb_log_file_size (deprecated)

  Log file size is set according to the automatically configured buffer pool size, as shown in the following table:

  Table 17.10 Automatically Configured Log File Size

  Buffer Pool Size	Log File Size
  Less than 8GB	512MB
  8GB to 128GB	1024MB
  Greater than 128GB	2048MB

  
  

• innodb_log_files_in_group (deprecated)

  The number of log files is determined according to the automatically configured buffer pool size, as shown in the following table:

  Table 17.11 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

  
  
  Note

  The minimum value for innodb_log_files_in_group value is 2; this lower limit is enforced if the rounded buffer pool size value is less than this number.

• innodb_flush_method

  The flush method is set to O_DIRECT_NO_FSYNC when the server is started with --innodb-dedicated-server. If O_DIRECT_NO_FSYNC is not available, the default value for innodb_flush_method.

  InnoDB uses O_DIRECT during flushing I/O, but skips the fsync() system call after each write operation.

  Warning

  Prior to MySQL 8.0.14, O_DIRECT_NO_FSYNC was 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 one of the variables listed previously is set explicitly in an option file or elsewhere, this explicit value is used, and a startup warning similar to this one 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.

Setting one variable explicitly does not prevent the automatic configuration of other options.

If the server is started with --innodb-dedicated-server and innodb_buffer_pool_size is set explicitly, variable settings based on buffer pool size use the buffer pool size value calculated according to the amount of memory detected on the server rather than the explicitly defined buffer pool size value.

Note

Automatic configuration settings are applied by --innodb-dedicated-server only when the MySQL server is started. If you later set any of the affected variables explicitly, this overrides its predetermined value, and the value that was explicitly set is applied. Setting one of these variables to DEFAULT causes it to be set to the actual default value as shown in the variable's description in the Manual, and does not cause it to revert to the value set by --innodb-dedicated-server. The corresponding system variable innodb_dedicated_server is changed only by starting the server with --innodb-dedicated-server (or with --innodb-dedicated-server=ON or --innodb-dedicated-server=OFF); it is otherwise read-only.