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MySQL性能优化之swap占用高_MySQL

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Jun 01, 2016 pm 01:28 PM

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MySQL性能优化之swap占用高

在MySQL的大数据量测试时，发现MySQL单表数据约超过4000万行时出现性能拐点。查询性能逐步下降，但下降还算缓慢。

继续添加数据，又出现一次明显的性能拐点。性能可谓是陡降，磁盘IO显著上升，开始使用交换分区。

此时MySQL的数据文件和内存一般大！这不太可能吧，当数据文件和内存一般大时就会出现性能下降？那以前服务器内存小的时候，MySQL岂不是不用干了？

部分内存是被操作系统吃了。手动干掉操作系统的文件缓存`echo 3 > /proc/sys/vm/drop_caches`，以为这样会让MySQL可用内存更多。但结果并未见好转，反而是缓存刚被清是性能更差了。

经过一轮搜索，原来是需要告诉操作系统尽可能的不要使用磁盘作交换：`echo 0 > /proc/sys/vm/swappiness`（更新到系统配置，在/etc/sysctl.conf上添加vm.swappiness = 0）。

此值默认为60，即(60%)。当然，设为0并非禁用，而是最大限度地使用物理内存。

OK，加此设置之后，MySQL在更多数据量时也未出现swap交换的现象、性能随数据量的增加平缓下降

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