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MySQL性能调优之Memory or SSD?

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Jun 07, 2016 pm 05:13 PM

SLC因为速度快，使用寿命长，一般被用在企业级SSD上。而MLC则多用在消费级市场，如workstation。Fusion-io开发出一种管理MLC闪存

当一个传统的向外扩展的方式对于MySQL来讲变得流行，看看我们不得不扩充哪一方面（便宜的内存？快速存储？更好的电源效率？）将会变得非常有趣。这里确实有很多种选择——我每周大概会遇到一个客户使用Fushion-IO 卡。然而，我却看到了他们一个有趣的选择——他们选择购买一个SSD，当他们每秒仍然能读取很多页的时候（这时，我宁愿选择购买内存来取代），而使用存储驱动器做“写操作”使用。

在这里，我提出几个参考标准来供你确认是否是以上我说的这种情况：

Percona-XtraDB-9.1 release

Sysbench(开源性能测试工具)的OLTP有8千万行的“工作量”（大概等同于18GB的数据+索引）

XFS 文件系统选择nobarrier选项安装

测试运行具有：

1. 带有BBU的RAID 10硬盘超过8块（所谓BBU，社区的解释是在掉电的情况下，能够cache数据72h，当机器供电正常，再从cache中将数据写入磁盘）

2. Inter SSD X25-E 32GB

3. FushionIO 320GB MLC【1】

对于每一次测试，在运行的时候将缓冲池设置在2G到22G之间（为了和合适的内存比较性能）

硬件配置：

Dell PowerEdgeR900

4 QuadCoreIntel(R) Xeon(R) CPU E7320 @ 2.13GHz (16 cores in total)

32GB of RAM

RAID10 on 8disks 2.5” 15K RPMS

FusionIO 160GBSLC

FusionIO 320GBMLC

OS:

CentOS 5.5

XFS filesystem

开始，我们对RAID 10的存储做一个测试以建立一个基线。Y轴是每秒传输的数据（传输速率，它越大越好）。X轴是innodb_buffer_pool_size的大小。

我特地挑选了关于该测试中的三个有趣的点

A点，当数据完全符合缓冲池大小（最佳性能）。一旦你达到该点，简直就像内存的进一步增加，了解该信息很重要。

B坐标出现在当数据刚开始超过缓冲池的大小。这对于许多用户来讲是最让人头疼的一点了。因为当内存下降仅10%，而性能却比原来降低了2.6倍。在产品中，这通常应对着这样的说辞——“上个星期一切看起来都还OK，但它却正在变得越来越慢！”。我想建议你，增加内存是迄今为止最好的做法，在这种情况下。

C点展示数据大约是缓冲池三倍的地方。它是一个有趣的点，既然你不能够计算出内存的花费（可能不了解未来遇到瓶颈需要耗费多少购买内存的成本），这是购买一个SSD可能更为合适。

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