Optimizing InnoDB
Disk I/O
If you follow the best practices for database design and the tuning techniques for SQL operations, but your database is still slowed by heavy disk I/O activity, explore these low-level techniques related to disk I/O. 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.
- When table data is cached in the
InnoDB
buffer pool, it can be processed over and over by queries without requiring any disk I/O. Specify the size of the buffer pool with theinnodb_buffer_pool_size
option. This memory area is important enough that busy databases often specify a size approximately 80% of the amount of physical memory. For more information, see , "TheInnoDB
Buffer Pool". - In some versions of GNU/Linux and Unix, flushing files to disk with the Unix
fsync()
call (whichInnoDB
uses by default) and similar methods is surprisingly slow. If database write performance is an issue, conduct benchmarks with theinnodb_flush_method
parameter set toO_DSYNC
. - When using the
InnoDB
storage engine on Solaris 10 for x86_64 architecture (AMD Opteron), use direct I/O forInnoDB
-related files, to avoid degradation ofInnoDB
performance. To use direct I/O for an entire UFS file system used for storingInnoDB
-related files, mount it with theforcedirectio
option; seemount_ufs(1M)
. (The default on Solaris 10/x86_64 is not to use this option.) To apply direct I/O only toInnoDB
file operations rather than the whole file system, setinnodb_flush_method = O_DIRECT
. With this setting,InnoDB
callsdirectio()
instead offcntl()
for I/O to data files (not for I/O to log files). - When using the
InnoDB
storage engine with a largeinnodb_buffer_pool_size
value on any release of Solaris 2.6 and up and any platform (sparc/x86/x64/amd64), conduct benchmarks withInnoDB
data files and log files on raw devices or on a separate direct I/O UFS file system, using theforcedirectio
mount option as described earlier. (It is necessary to use the mount option rather than settinginnodb_flush_method
if you want direct I/O for the log files.) Users of the Veritas file system VxFS should use theconvosync=direct
mount option.Do not place other MariaDB data files, such as those for
MyISAM
tables, on a direct I/O file system. Executables or libraries must not be placed on a direct I/O file system. - If you have additional storage devices available to set up a RAID configuration or symbolic links to different disks, , "Optimizing Disk I/O" for additional low-level I/O tips.
- If throughput drops periodically because of
InnoDB
checkpoint operations, consider increasing the value of theinnodb_io_capacity
configuration option. Higher values cause more frequent flushing, avoiding the backlog of work that can cause dips in throughput. - If the system is not falling behind with
InnoDB
flushing operations, consider lowering the value of theinnodb_io_capacity
configuration option. Typically, you keep this option value as low as practical, but not so low that it causes periodic drops in throughput as mentioned in the preceding bullet. In a typical scenario where you could lower the option value, you might see a combination like this in the output fromSHOW ENGINE INNODB STATUS
:- History list length low, below a few thousand.
- Insert buffer merges close to rows inserted.
- Modified pages in buffer pool consistently well below
innodb_max_dirty_pages_pct
of the buffer pool. (Measure at a time when the server is not doing bulk inserts; it is normal during bulk inserts for the modified pages percentage to rise significantly.) Log sequence number - Last checkpoint
is at less than 7/8 or ideally less than 6/8 of the total size of theInnoDB
log files.
- Other
InnoDB
configuration options to consider when tuning I/O-bound workloads includeinnodb_adaptive_flushing
,innodb_change_buffer_max_size
,innodb_change_buffering
,innodb_flush_neighbors
,innodb_log_buffer_size
,innodb_log_file_size
,innodb_lru_scan_depth
,innodb_max_dirty_pages_pct
,innodb_max_purge_lag
,innodb_open_files
,innodb_page_size
,innodb_random_read_ahead
,innodb_read_ahead_threshold
,innodb_read_io_threads
,innodb_rollback_segments
,innodb_write_io_threads
, andsync_binlog
.