The first decisions to make about
configuration involve the configuration of data files, log files,
page size, and memory buffers, which should be configured before
InnoDB. Modifying the
InnoDB is initialized may
involve non-trivial procedures.
This section provides information about specifying
InnoDB settings in a configuration file,
InnoDB initialization information, and
important storage considerations.
Because MySQL uses data file, log file, and page size settings
InnoDB, it is recommended that
you define these settings in an option file that MySQL reads at
startup, prior to initializing
InnoDB is initialized when the
MySQL server is started for the first time.
You can place
InnoDB options in the
[mysqld] group of any option file that your
server reads when it starts. The locations of MySQL option files
are described in Section 220.127.116.11, “Using Option Files”.
InnoDB initialization information
during startup, start mysqld from a command
prompt, which prints initialization information to the console.
For example, on Windows, if mysqld is located
C:\Program Files\MySQL\MySQL Server
8.0\bin, start the MySQL server like
C:\> "C:\Program Files\MySQL\MySQL Server 8.0\bin\mysqld" --console
On Unix-like systems, mysqld is located in
bin directory of your MySQL
shell> bin/mysqld --user=mysql &
If you do not send server output to the console, check the error
log after startup to see the initialization information
InnoDB printed during the startup process.
For information about starting MySQL using other methods, see Section 2.10.5, “Starting and Stopping MySQL Automatically”.
InnoDB does not open all user tables and
associated data files at startup. However,
InnoDB does check for the existence of
tablespace files referenced in the data dictionary. If a
tablespace file is not found,
an error and continues the startup sequence. Tablespace files
referenced in the redo log may be opened during crash recovery
for redo application.
Review the following storage-related considerations before proceeding with your startup configuration.
In some cases, you can improve database performance by placing data and log files on separate physical disks. You can also use raw disk partitions (raw devices) for
InnoDBdata files, which may speed up I/O. See Using Raw Disk Partitions for the System Tablespace.
InnoDBis a transaction-safe (ACID compliant) storage engine with commit, rollback, and crash-recovery capabilities to protect user data. However, it cannot do so if the underlying operating system or hardware does not work as advertised. Many operating systems or disk subsystems may delay or reorder write operations to improve performance. On some operating systems, the very
fsync()system call that should wait until all unwritten data for a file has been flushed might actually return before the data has been flushed to stable storage. Because of this, an operating system crash or a power outage may destroy recently committed data, or in the worst case, even corrupt the database because write operations have been reordered. If data integrity is important to you, perform “pull-the-plug” tests before using anything in production. On macOS,
InnoDBuses a special
fcntl()file flush method. Under Linux, it is advisable to disable the write-back cache.
On ATA/SATA disk drives, a command such
hdparm -W0 /dev/hdamay work to disable the write-back cache. Beware that some drives or disk controllers may be unable to disable the write-back cache.
With regard to
InnoDBrecovery capabilities that protect user data,
InnoDBuses a file flush technique involving a structure called the doublewrite buffer, which is enabled by default (
innodb_doublewrite=ON). The doublewrite buffer adds safety to recovery following an unexpected exit or power outage, and improves performance on most varieties of Unix by reducing the need for
fsync()operations. It is recommended that the
innodb_doublewriteoption remains enabled if you are concerned with data integrity or possible failures. For information about the doublewrite buffer, see Section 15.11.1, “InnoDB Disk I/O”.
Before using NFS with
InnoDB, review potential issues outlined in Using NFS with MySQL.
option defines the name, size, and attributes of
InnoDB system tablespace data files. If you
do not configure this option prior to initializing the MySQL
server, the default behavior is to create a single
auto-extending data file, slightly larger than 12MB, named
mysql> SHOW VARIABLES LIKE 'innodb_data_file_path'; +-----------------------+------------------------+ | Variable_name | Value | +-----------------------+------------------------+ | innodb_data_file_path | ibdata1:12M:autoextend | +-----------------------+------------------------+
The full data file specification syntax includes the file name,
autoextend attribute, and
File sizes are specified in kilobytes, megabytes, or gigabytes
G to the size value. If specifying the data
file size in kilobytes, do so in multiples of 1024. Otherwise,
kilobyte values are rounded to nearest megabyte (MB) boundary.
The sum of file sizes must be, at a minimum, slightly larger
You can specify more than one data file using a semicolon-separated list. For example:
attributes can be used only for the data file that is specified
autoextend attribute is specified,
the data file automatically increases in size by 64MB increments
as space is required. The
variable controls the increment size.
To specify a maximum size for an auto-extending data file, use
max attribute following the
autoextend attribute. Use the
max attribute only in cases where
constraining disk usage is of critical importance. The following
ibdata1 to grow to a
limit of 500MB:
A minimum file size is enforced for the
first system tablespace data file to ensure
that there is enough space for doublewrite buffer pages. The
following table shows minimum file sizes for each
InnoDB page size. The default
InnoDB page size is 16384 (16KB).
|Page Size (innodb_page_size)||Minimum File Size|
|16384 (16KB) or less||3MB|
If your disk becomes full, you can add a data file on another disk. For instructions, see Resizing the System Tablespace.
The size limit for individual files is determined by your operating system. You can set the file size to more than 4GB on operating systems that support large files. You can also use raw disk partitions as data files. See Using Raw Disk Partitions for the System Tablespace.
InnoDB is not aware of the file system
maximum file size, so be cautious on file systems where the
maximum file size is a small value such as 2GB.
System tablespace files are created in the data directory by
datadir). To specify
an alternate location, use the
For example, to create a system tablespace data file in a
myibdata, use this
[mysqld] innodb_data_home_dir = /myibdata/ innodb_data_file_path=ibdata1:50M:autoextend
A trailing slash is required when specifying a value for
InnoDB does not create directories, so ensure
that the specified directory exists before you start the server.
Also, ensure sure that the MySQL server has the proper access
rights to create files in the directory.
InnoDB forms the directory path for each data
file by textually concatenating the value of
innodb_data_home_dir to the
data file name. If
innodb_data_home_dir is not
defined, the default value is “./”, which is the
data directory. (The MySQL server changes its current working
directory to the data directory when it begins executing.)
Alternatively, you can specify an absolute path for system tablespace data files. The following configuration is equivalent to the preceding one:
When you specify an absolute path for
setting is not concatenated with the
System tablespace files are created in the specified absolute
path. The specified directory must exist before you start the
As of MySQL 8.0.20, the doublewrite buffer storage area resides
in doublewrite files, which provides flexibility with respect to
the storage location of doublewrite pages. In previous releases,
the doublwrite buffer storage area resided in the system
defines the directory where
doublewrite files at startup. If no directory is specified,
doublewrite files are created in the
which defaults to the data directory if unspecified.
Other doublewrite buffer variables permit defining the number of doublewrite files, the number of pages per thread, and the doublewrite batch size. For more information about doublewrite buffer configuration, see Section 15.6.4, “Doublewrite Buffer”.
InnoDB creates two 5MB redo log files named
ib_logfile1 in the data directory by
The following options can be used to modify the default configuration:
You might use this option to place
InnoDBlog files in a different physical storage location than
InnoDBdata files to avoid potential I/O resource conflicts. For example:
[mysqld] innodb_log_group_home_dir = /dr3/iblogsNote
InnoDBdoes not create directories, so make sure that the log directory exists before you start the server. Use the Unix or DOS
mkdircommand to create any necessary directories.
Make sure that the MySQL server has the proper access rights to create files in the log directory. More generally, the server must have access rights in any directory where it needs to create log files.
innodb_log_files_in_groupdefines the number of log files in the log group. The default and recommended value is 2.
innodb_log_file_sizedefines the size in bytes of each log file in the log group. The combined log file size (
innodb_log_files_in_group) cannot exceed the maximum value, which is slightly less than 512GB. A pair of 255 GB log files, for example, approaches the limit but does not exceed it. The default log file size is 48MB. Generally, the combined size of the log files should be large enough that the server can smooth out peaks and troughs in workload activity, which often means that there is enough redo log space to handle more than an hour of write activity. A larger log file size means less checkpoint flush activity in the buffer pool, which reduces disk I/O. For additional information, see Section 8.5.4, “Optimizing InnoDB Redo Logging”.
Undo logs, by default, reside in two undo tablespaces created when the MySQL instance is initialized.
variable defines the path where
creates default undo tablespaces. If that variable is undefined,
default undo tablespaces are created in the data directory. The
is not dynamic. Configuring it requires restarting the server.
The I/O patterns for undo logs make undo tablespaces good candidates for SSD storage.
For information about configuring additional undo tablespaces, see Section 18.104.22.168, “Undo Tablespaces”.
The global temporary tablespace stores rollback segments for changes made to user-created temporary tables.
A single auto-extending global temporary tablespace data file
ibtmp1 in the
by default. The initial file size is slightly larger than 12MB.
option specifies the path, file name, and file size for global
temporary tablespace data files. File size is specified in KB,
MB, or GB by appending K, M, or G to the size value. The file
size or combined file size must be slightly larger than 12MB.
To specify an alternate location for global temporary tablespace
data files, configure the
option at startup.
In MySQL 8.0.15 and earlier, session temporary tablespaces store
user-created temporary tables and internal temporary tables
created by the optimizer when
configured as the on-disk storage engine for internal temporary
From MySQL 8.0.16,
InnoDB is always used as
the on-disk storage engine for internal temporary tables.
variable defines the location where
creates session temporary tablespaces. The default location is
#innodb_temp directory in the data
To specify an alternate location for session temporary
tablespaces, configure the
variable at startup. A fully qualified path or path relative to
the data directory is permitted.
specifies the page size for all
tablespaces in a MySQL instance. This value is set when the
instance is created and remains constant afterward. Valid values
are 64KB, 32KB, 16KB (the default), 8KB, and 4KB. Alternatively,
you can specify page size in bytes (65536, 32768, 16384, 8192,
The default 16KB page size is appropriate for a wide range of
workloads, particularly for queries involving table scans and
DML operations involving bulk updates. Smaller page sizes might
be more efficient for OLTP workloads involving many small
writes, where contention can be an issue when a single page
contains many rows. Smaller pages can also be more efficient for
SSD storage devices, which typically use small block sizes.
InnoDB page size close to the
storage device block size minimizes the amount of unchanged data
that is rewritten to disk.
MySQL allocates memory to various caches and buffers to improve
performance of database operations. When allocating memory for
InnoDB, always consider memory required by
the operating system, memory allocated to other applications,
and memory allocated for other MySQL buffers and caches. For
example, if you use
MyISAM tables, consider
the amount of memory allocated for the key buffer
key_buffer_size). For an
overview of MySQL buffers and caches, see
Section 22.214.171.124, “How MySQL Uses Memory”.
Buffers specific to
InnoDB are configured
using the following parameters:
innodb_buffer_pool_sizedefines size of the buffer pool, which is the memory area that holds cached data for
InnoDBtables, indexes, and other auxiliary buffers. The size of the buffer pool is important for system performance, and it is typically recommended that
innodb_buffer_pool_sizeis configured to 50 to 75 percent of system memory. The default buffer pool size is 128MB. For additional guidance, see Section 126.96.36.199, “How MySQL Uses Memory”. For information about how to configure
InnoDBbuffer pool size, see Section 188.8.131.52, “Configuring InnoDB Buffer Pool Size”. Buffer pool size can be configured at startup or dynamically.
On systems with a large amount of memory, you can improve concurrency by dividing the buffer pool into multiple buffer pool instances. The number of buffer pool instances is controlled by the by
innodb_buffer_pool_instancesoption. By default,
InnoDBcreates one buffer pool instance. The number of buffer pool instances can be configured at startup. For more information, see Section 184.108.40.206, “Configuring Multiple Buffer Pool Instances”.
innodb_log_buffer_sizedefines the size of the buffer that
InnoDBuses to write to the log files on disk. The default size is 16MB. A large log buffer enables large transactions to run without writing the log to disk before the transactions commit. If you have transactions that update, insert, or delete many rows, you might consider increasing the size of the log buffer to save disk I/O.
innodb_log_buffer_sizecan be configured at startup. For related information, see Section 8.5.4, “Optimizing InnoDB Redo Logging”.
On 32-bit GNU/Linux x86, if memory usage is set too high,
glibc may permit the process heap to grow
over the thread stacks, causing a server failure. It is a risk
if the memory allocated to the mysqld
process for global and per-thread buffers and caches is close
to or exceeds 2GB.
A formula similar to the following that calculates global and per-thread memory allocation for MySQL can be used to estimate MySQL memory usage. You may need to modify the formula to account for buffers and caches in your MySQL version and configuration. For an overview of MySQL buffers and caches, see Section 220.127.116.11, “How MySQL Uses Memory”.
innodb_buffer_pool_size + key_buffer_size + max_connections*(sort_buffer_size+read_buffer_size+binlog_cache_size) + max_connections*2MB
Each thread uses a stack (often 2MB, but only 256KB in MySQL
binaries provided by Oracle Corporation.) and in the worst
case also uses
read_buffer_size additional memory.
On Linux, if the kernel is enabled for large page support,
InnoDB can use large pages to allocate memory
for its buffer pool. See Section 18.104.22.168, “Enabling Large Page Support”.