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如何使用sql profiler性能分析器 mysql 的 sql 性能分析器主要用途是显示 sql 执行的整个过程中各项资源的使用情况。
分析器可以更好的展示出不良 sql 的性能问题所在。 下面我们举例介绍一下 mysql sql profiler 的使用方法：    首先，开启 mysql sql profiler mysql> select @@profiling; +-------------+ | @@profiling | +-------------+ | 0 | +-------------+ 1 row in set (0.00 sec) mysql> set profiling = 1; query ok, 0 rows affected (0.00 sec) mysql> select @@profiling; +-------------+ | @@profiling | +-------------+ | 1 | +-------------+ 1 row in set (0.00 sec) 默认情况下 profiling 的值为 0 表示 mysql sql profiler 处于 off 状态，开启 sql 性能分析器后 profiling 的值为 1.    通过 sql 性能分析器，我们来对比一下 下列语句前后 2 次执行过程的差异，对我们了解 sql 的详细执行过程是非常有帮助的。 mysql> create table t_engines select * from t_engines1; query ok, 57344 rows affected (0.10 sec) records: 57344 duplicates: 0 warnings: 0 mysql> select count(*) from t_engines; +----------+ | count(*) | +----------+ | 57344 | +----------+ 1 row in set (0.00 sec) mysql> select count(*) from t_engines; +----------+ | count(*) | +----------+ | 57344 | +----------+ 1 row in set (0.00 sec) mysql> show profiles; +----------+------------+-------------------------------------------------+ | query_id | duration | query | +----------+------------+-------------------------------------------------+ | 26 | 0.10213775 | create table t_engines select * from t_engines1 | | 27 | 0.00032775 | select count(*) from t_engines | | 28 | 0.00003850 | select count(*) from t_engines | +----------+------------+-------------------------------------------------+ 15 rows in set (0.01 sec)mysql> show profile for query 27; +--------------------------------+------------+ | status | duration | +--------------------------------+------------+ | (initialization) | 0.00000425 | | checking query cache for query | 0.00004050 | | checking permissions | 0.00001050 | | opening tables | 0.00018250 | | system lock | 0.00000450 | | table lock | 0.00001775 | | init | 0.00001075 | | optimizing | 0.00000550 | | executing | 0.00002775 | | end | 0.00000450 | | query end | 0.00000325 | | storing result in query cache | 0.00000400 | | freeing items | 0.00000400 | | closing tables | 0.00000500 | | logging slow query | 0.00000300 | +--------------------------------+------------+ 15 rows in set (0.00 sec) mysql> show profile for query 28; +-------------------------------------+------------+ | status | duration | +-------------------------------------+------------+ | (initialization) | 0.00000350 | | checking query cache for query | 0.00000750 | | checking privileges on cached query | 0.00000500 | | checking permissions | 0.00000525 | | sending cached result to client | 0.00001275 | | logging slow query | 0.00000450 | +-------------------------------------+------------+ 6 rows in set (0.00 sec)mysql> select sum( format(duration, 6)) as duration from information_schema.profiling where query_id =27 order by seq; +----------+ | duration | +----------+ | 0.000326 | +----------+ 1 row in set (0.00 sec) mysql> select sum( format(duration, 6)) as duration from information_schema.profiling where query_id =28 order by seq; +----------+ | duration | +----------+ | 0.000039 | +----------+ 1 row in set (0.00 sec) mysql>    从上面的例子中我们可以清晰的看出 2 次执行 count 语句的差别， show profile for query 27 展现的是第一次 count 统计的执行过程，包含了 opening tables 、 table lock 等操作 。而 show profile for query 28 展示了第二次 count 统计的执行过程 , 第二次 count 直接从查询缓存中返回 count 统计结果，通过对比 2 次统计的总执行时间发现，缓存读的速度接近物理读的 10 倍。通过使用 sql 性能分析器可以帮助我们对一些比较难以确定性能问题的 sql 进行诊断，找出问题根源。  bitscn.com