MySQL服务器安装完以后如何调节性能

原文做者： Peter Zaitsev
原文来源： http://www.mysqlperformanceblog.com/2006/09/29/what-to-tune-in-mysql-server-after-installation
译者：叶金荣（Email:），转载请注明译者和出处，而且不能用于商业用途，违者必究。

My favorite question during Interview for people to work as MySQL DBAs or be involved with MySQL Performance in some way is to ask them what should be tuned in MySQL Server straight after installation, assuming it was installed with default settings.

在面试MySQL DBA或者那些打算作MySQL性能优化的人时，我最喜欢问题是：MySQL服务器按照默认设置安装完以后，应该作哪些方面的调节呢？

I’m surprised how many people fail to provide any reasonable answer to this question, and how many servers are where in wild which are running with default settings.

令我很惊讶的是，有多少人对这个问题没法给出合理的答案，又有多少服务器都运行在默认的设置下。

Even though you can tune quite a lot of variables in MySQL Servers only few of them are really important for most common workload. After you get these settings right other changes will most commonly offer only incremental performance improvements.

尽管你能够调节不少MySQL服务器上的变量，可是在大多数一般的工做负载下，只有少数几个才真正重要。若是你把这些变量设置正确了，那么修改其余变量最多只能对系统性能改善有必定提高。

key_buffer_size – Very important if you use MyISAM tables. Set up to 30-40% of available memory if you use MyISAM tables exclusively. Right size depends on amount of indexes, data size and workload – remember MyISAM uses OS cache to cache the data so you need to leave memory for it as well, and data can be much larger than indexes in many cases. Check however if all of key_buffer is used over time – it is not rare to see key_buffer being set to 4G while combined size of .MYI files is just 1GB. This would be just a waste. If you use few MyISAM tables you’ll want to keep it lower but still at least 16-32Mb so it is large enough to accommodate indexes for temporary tables which are created on disk.

key_buffer_size – 这对MyISAM表来讲很是重要。若是只是使用MyISAM表，能够把它设置为可用内存的 30-40%。合理的值取决于索引大小、数据量以及负载 — 记住，MyISAM表会使用操做系统的缓存来缓存数据，所以须要留出部份内存给它们，不少状况下数据比索引大多了。尽管如此，须要老是检查是否全部的 key_buffer 都被利用了 — .MYI 文件只有 1GB，而 key_buffer 却设置为 4GB 的状况是很是少的。这么作太浪费了。若是你不多使用MyISAM表，那么也保留低于 16-32MB 的 key_buffer_size 以适应给予磁盘的临时表索引所需。

innodb_buffer_pool_size This is very important variable to tune if you’re using Innodb tables. Innodb tables are much more sensitive to buffer size compared to MyISAM. MyISAM may work kind of OK with default key_buffer_size even with large data set but it will crawl with default innodb_buffer_pool_size. Also Innodb buffer pool caches both data and index pages so you do not need to leave space for OS cache so values up to 70-80% of memory often make sense for Innodb only installations. Same rules as for key_buffer apply – if you have small data set and it is not going to grow dramatically do not oversize innodb_buffer_pool_size you might find better use for memory available.

innodb_buffer_pool_size – 这对Innodb表来讲很是重要。Innodb相比MyISAM表对缓冲更为敏感。MyISAM能够在默认的 key_buffer_size 设置下运行的能够，然而Innodb在默认的 innodb_buffer_pool_size 设置下却跟蜗牛似的。因为Innodb把数据和索引都缓存起来，无需留给操做系统太多的内存，所以若是只须要用Innodb的话则能够设置它高达 70-80% 的可用内存。一些应用于 key_buffer 的规则有 — 若是你的数据量不大，而且不会暴增，那么无需把 innodb_buffer_pool_size 设置的太大了。

innodb_additional_pool_size This one does not really affect performance too much, at least on OS with decent memory allocators. Still you might want to have it 20MB (sometimes larger) so you can see how much memory Innodb allocates for misc needs.

innodb_additional_pool_size – 这个选项对性能影响并不太多，至少在有差很少足够内存可分配的操做系统上是这样。不过若是你仍然想设置为 20MB(或者更大)，所以就须要看一下Innodb其余须要分配的内存有多少。

innodb_log_file_size Very important for write intensive workloads especially for large data sets. Larger sizes offer better performance but increase recovery times so be careful. I normally use values 64M-512M depending on server size.

innodb_log_file_size 在高写入负载尤为是大数据集的状况下很重要。这个值越大则性能相对越高，可是要注意到可能会增长恢复时间。我常常设置为 64-512MB，跟据服务器大小而异。

innodb_log_buffer_size Default for this one is kind of OK for many workloads with medium write load and shorter transactions. If you have update activity spikes however or work with blobs a lot you might want to increase it. Do not set it too high however as it would be waste of memory – it is flushed every 1 sec anyway so you do not need space for more than 1 sec worth of updates. 8MB-16MB are typically enough. Smaller installations should use smaller values.

innodb_log_buffer_size 默认的设置在中等强度写入负载以及较短事务的状况下，服务器性 能还能够。若是存在更新操做峰值或者负载较大，就应该考虑加大它的值了。若是它的值设置过高了，可能会浪费内存 — 它每秒都会刷新一次，所以无需设置超过1秒所需的内存空间。一般 8-16MB 就足够了。越小的系统它的值越小。

innodb_flush_logs_at_trx_commit Crying about Innodb being 100 times slower than MyISAM ? You probably forgot to adjust this value. Default value of 1 will mean each update transaction commit (or each statement outside of transaction) will need to flush log to the disk which is rather expensive, especially if you do not have Battery backed up cache. Many applications, especially those moved from MyISAM tables are OK with value 2 which means do not flush log to the disk but only flush it to OS cache. The log is still flushed to the disk each second so you normally would not loose more than 1-2 sec worth of updates. Value 0 is a bit faster but is a bit less secure as you can lose transactions even in case MySQL Server crashes. Value 2 only cause data loss with full OS crash.

innodb_flush_logs_at_trx_commit 是否为Innodb比MyISAM慢1000倍而头大？看来也许你忘了修改这个参数了。默认值是 1，这意味着每次提交的更新事务（或者每一个事务以外的语句）都会刷新到磁盘中，而这至关耗费资源，尤为是没有电池备用缓存时。不少应用程序，尤为是从 MyISAM转变过来的那些，把它的值设置为 2 就能够了，也就是不把日志刷新到磁盘上，而只刷新到操做系统的缓存上。日志仍然会每秒刷新到磁盘中去，所以一般不会丢失每秒1-2次更新的消耗。若是设置 为 0 就快不少了，不过也相对不安全了 — MySQL服务器崩溃时就会丢失一些事务。设置为 2 指挥丢失刷新到操做系统缓存的那部分事务。

table_cache – Opening tables can be expensive. For example MyISAM tables mark MYI header to mark table as currently in use. You do not want this to happen so frequently and it is typically best to size your cache so it is large enough to keep most of your tables open. It uses some OS resources and some memory but for modern hardware it is typically not the problem. 1024 is good value for applications with couple hundreds tables (remember each connection needs its own entry) if you have many connections or many tables increase it larger. I’ve seen values over 100.000 used.

table_cache — 打开一个表的开销可能很大。例如MyISAM把MYI文件头标志该表正在使用中。你确定不但愿这种操做太频繁，因此一般要加大缓存数量，使得足以最大限度 地缓存打开的表。它须要用到操做系统的资源以及内存，对当前的硬件配置来讲固然不是什么问题了。若是你有200多个表的话，那么设置为 1024 也许比较合适（每一个线程都须要打开表），若是链接数比较大那么就加大它的值。我曾经见过设置为 100,000 的状况。

thread_cache Thread creation/destructions can be expensive, which happen at each connect/disconnect. I normally set this value to at least 16. If application has large jumps in amount of concurrent connections and I see fast growth of
Threads_Created variable I boost it higher. The goal is not to have threads created in normal operation.

thread_cache — 线程的建立和销毁的开销可能很大，由于每一个线程的链接/断开都须要。我一般至少设置为 16。若是应用程序中有大量的跳跃并发链接而且 Threads_Created 的值也比较大，那么我就会加大它的值。它的目的是在一般的操做中无需建立新线程。

query_cache If your application is read intensive and you do not have application level caches this can be great help. Do not set it too large as it may slow things down as its maintenance may get expensive. Values from 32M to 512M normally make sense. Check it however after a while and see if it is well used. For certain workloads cache hit ratio is lower than would justify having it enabled.

query_cache — 若是你的应用程序有大量读，并且没有应用程序级别的缓存，那么这颇有用。不要把它设置太大了，由于想要维护它也须要很多开销，这会致使MySQL变慢。通 常设置为 32-512Mb。设置完以后最好是跟踪一段时间，查看是否运行良好。在必定的负载压力下，若是缓存命中率过低了，就启用它。

Note: as you can see all of these are global variables. These variables depend on hardware and mix of storage engines, while per session variables are typically workload specific. If you have simple queries there is no reason to increase sort_buffer_size even if you have 64GB of memory to waste. Furthermore doing so may decrease performance.
I normally leave per session variable tuning to second step after I can analyze workload.

注意：就像你看到的上面这些全局表量，它们都是依据硬件配置以及不一样的存储引擎而不一样，可是会话变量一般是根据不一样的负载来设定的。若是你只有一些简单的查询，那么就无需增长 sort_buffer_size 的值了，尽管你有 64GB 的内存。搞很差也许会下降性能。
我一般在分析系统负载后才来设置会话变量。

P.S Note MySQL distribution contains bunch of sample my.cnf files which may be great templates to use. Typically they would already be much better than defaults if you chose correct one.

P.S，MySQL的发行版已经包含了各类 my.cnf 范例文件了，能够做为配置模板使用。一般这比你使用默认设置好的多了。