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14.2.11. InnoDB Performance Tuning Tips

  • If the Unix top tool or the Windows Task Manager shows that the CPU usage percentage with your workload is less than 70%, your workload is probably disk-bound. Maybe you are making too many transaction commits, or the buffer pool is too small. Making the buffer pool bigger can help, but do not set it equal to more than 80% of physical memory.

  • Wrap several modifications into one transaction. InnoDB must flush the log to disk at each transaction commit if that transaction made modifications to the database. The rotation speed of a disk is typically at most 167 revolutions/second, which constrains the number of commits to the same 167th of a second if the disk does not “fool” the operating system.

  • If you can afford the loss of some of the latest committed transactions if a crash occurs, you can set the innodb_flush_log_at_trx_commit parameter to 0. InnoDB tries to flush the log once per second anyway, although the flush is not guaranteed.

  • Make your log files big, even as big as the buffer pool. When InnoDB has written the log files full, it has to write the modified contents of the buffer pool to disk in a checkpoint. Small log files cause many unnecessary disk writes. The drawback of big log files is that the recovery time is longer.

  • Make the log buffer quite large as well (on the order of 8MB).

  • Use the VARCHAR data type instead of CHAR if you are storing variable-length strings or if the column may contain many NULL values. A CHAR(N) column always takes N characters to store data, even if the string is shorter or its value is NULL. Smaller tables fit better in the buffer pool and reduce disk I/O.

    When using row_format=compact (the default InnoDB record format in MySQL 5.1) and variable-length character sets, such as utf8 or sjis, CHAR(N) will occupy a variable amount of space, at least N bytes.

  • In some versions of GNU/Linux and Unix, flushing files to disk with the Unix fsync() call (which InnoDB uses by default) and other similar methods is surprisingly slow. If you are dissatisfied with database write performance, you might try setting the innodb_flush_method parameter to O_DSYNC. Although O_DSYNC seems to be slower on most systems, yours might not be one of them.

  • When using the InnoDB storage engine on Solaris 10 for x86_64 architecture (AMD Opteron), it is important to mount any filesystems used for storing InnoDB-related files using the forcedirectio option. (The default on Solaris 10/x86_64 is not to use this option.) Failure to use forcedirectio causes a serious degradation of InnoDB's speed and performance on this platform.

    When using the InnoDB storage engine with a large innodb_buffer_pool_size value on any release of Solaris 2.6 and up and any platform (sparc/x86/x64/amd64), a significant performance gain can be achieved by placing InnoDB data files and log files on raw devices or on a separate direct I/O UFS filesystem (using mount option forcedirectio; see mount_ufs(1M)). Users of the Veritas filesystem VxFS should use the mount option convosync=direct.

    Other MySQL data files, such as those for MyISAM tables, should not be placed on a direct I/O filesystem. Executables or libraries must not be placed on a direct I/O filesystem.

  • When importing data into InnoDB, make sure that MySQL does not have autocommit mode enabled because that requires a log flush to disk for every insert. To disable autocommit during your import operation, surround it with SET AUTOCOMMIT and COMMIT statements:

    SET AUTOCOMMIT=0;
    ... SQL import statements ...
    COMMIT;
    

    If you use the mysqldump option --opt, you get dump files that are fast to import into an InnoDB table, even without wrapping them with the SET AUTOCOMMIT and COMMIT statements.

  • Beware of big rollbacks of mass inserts: InnoDB uses the insert buffer to save disk I/O in inserts, but no such mechanism is used in a corresponding rollback. A disk-bound rollback can take 30 times as long to perform as the corresponding insert. Killing the database process does not help because the rollback starts again on server startup. The only way to get rid of a runaway rollback is to increase the buffer pool so that the rollback becomes CPU-bound and runs fast, or to use a special procedure. See Section 14.2.8.1, “Forcing InnoDB Recovery”.

  • Beware also of other big disk-bound operations. Use DROP TABLE and CREATE TABLE to empty a table, not DELETE FROM tbl_name.

  • Use the multiple-row INSERT syntax to reduce communication overhead between the client and the server if you need to insert many rows:

    INSERT INTO yourtable VALUES (1,2), (5,5), ...;
    

    This tip is valid for inserts into any table, not just InnoDB tables.

  • If you have UNIQUE constraints on secondary keys, you can speed up table imports by temporarily turning off the uniqueness checks during the import session:

    SET UNIQUE_CHECKS=0;
    ... import operation ...
    SET UNIQUE_CHECKS=1;
    

    For big tables, this saves a lot of disk I/O because InnoDB can use its insert buffer to write secondary index records in a batch.

  • If you have FOREIGN KEY constraints in your tables, you can speed up table imports by turning the foreign key checks off for the duration of the import session:

    SET FOREIGN_KEY_CHECKS=0;
    ... import operation ...
    SET FOREIGN_KEY_CHECKS=1;
    

    For big tables, this can save a lot of disk I/O.

  • If you often have recurring queries for tables that are not updated frequently, use the query cache:

    [mysqld]
    query_cache_type = ON
    query_cache_size = 10M
    

 
 
  Published under the terms of the GNU General Public License Design by Interspire