MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0
When the server is started with
--innodb-dedicated-server,
InnoDB automatically calculates values for and
sets the following system variables:
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_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of MySQL 8.0.30, and are superseded by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:
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 |
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.
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 |
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.
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.
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.
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.