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在5.1.X版本中,最多只会刷新100个脏页到磁盘、合并20个插入缓冲,即使磁盘有能力处理更多的请求,只能会处理这么多,这样在更新量较大的时候,脏页刷新就可能跟不上,导致性能下降。
但在5.5.X版本里,innodb_io_capacity参数可以动态调整刷新脏页的数量,这在一定程度上解决了这一问题。
innodb_io_capacity默认是200,单位是页,该参数的设置大小取决于硬盘的IOPS,即每秒每秒的输入输出量(或读写次数)。
可以动态调整参数:set global innodb_io_capacity=2000;
磁盘配置与innodb_io_capacity参数值
innodb_io_capacity | 磁盘配置 |
200 | 单盘SAS/SATA |
2000 | SAS*12 RAID 10 |
5000 | SSD |
50000 | FUSION-IO |
13.7.7.11. Controlling the Master Thread I/O Rate
The master thread in InnoDB is a thread that performs various tasks in the background. Most of these tasks are I/O related, such as flushing dirty pages from the buffer cache or writing changes from the insert buffer to the appropriate secondary indexes. The master thread attempts to perform these tasks in a way that does not adversely affect the normal working of the server. It tries to estimate the free I/O bandwidth available and tune its activities to take advantage of this free capacity. Historically, InnoDB has used a hard coded value of 100 IOPs (input/output operations per second) as the total I/O capacity of the server.
Beginning with InnoDB storage engine 1.0.4, a new configuration parameter indicates the overall I/O capacity available to InnoDB. The new parameter innodb_io_capacity
should be set to approximately the number of I/O operations that the system can perform per second. The value depends on your system configuration. When innodb_io_capacity
is set, the master threads estimates the I/O bandwidth available for background tasks based on the set value. Setting the value to 100
reverts to the old behavior.
You can set the value of innodb_io_capacity
to any number 100 or greater, and the default value is 200
. You can set the value of this parameter in the MySQL option file (myf
or my.ini
) or change it dynamically with the SET GLOBAL
command, which requires the SUPER
privilege.
本文标签: innodbiocapacity
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