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MySQL中使用SHOW PROFILE命令分析性能的用法整理

时间：2021-08-18 08:16:57 | 栏目：Mysql | 点击：次

show profile是由Jeremy Cole捐献给MySQL社区版本的。默认的是关闭的，但是会话级别可以开启这个功能。开启它可以让MySQL收集在执行语句的时候所使用的资源。为了统计报表,把profiling设为1
 

mysql> SET profiling = 1;

 
之后在运行一个查询

mysql> SELECT COUNT(DISTINCT actor.first_name) AS cnt_name, COUNT(*) AS cnt
-> FROM sakila.film_actor
-> INNER JOIN sakila.actor USING(actor_id)
-> GROUP BY sakila.film_actor.film_id
-> ORDER BY cnt_name DESC;
...
997 rows in set (0.03 sec)

 
这个执行语句的剖析信息存储在这个会话中。使用SHOW PROFILES进行查看。

mysql> SHOW PROFILES\G

*************************** 1. row ***************************
Query_ID: 1
Duration: 0.02596900
Query: SELECT COUNT(DISTINCT actor.first_name) AS cnt_name,...

 
你可以使用SHOW PROFILE语句来获取已经存储的剖析数据。如果不加参数，会显示状态以及它们持续的时间。

mysql> SHOW PROFILE;

+------------------------+-----------+
| Status | Duration |
+------------------------+-----------+
| (initialization) | 0.000005 |
| Opening tables | 0.000033 |
| System lock | 0.000037 |
| Table lock | 0.000024 |
| init | 0.000079 |
| optimizing | 0.000024 |
| statistics | 0.000079 |
| preparing | 0.00003 |
| Creating tmp table | 0.000124 |
| executing | 0.000008 |
| Copying to tmp table | 0.010048 |
| Creating sort index | 0.004769 |
| Copying to group table | 0.0084880 |
| Sorting result | 0.001136 |
| Sending data | 0.000925 |
| end | 0.00001 |
| removing tmp table | 0.00004 |
| end | 0.000005 |
| removing tmp table | 0.00001 |
| end | 0.000011 |
| query end | 0.00001 |
| freeing items | 0.000025 |
| removing tmp table | 0.00001 |
| freeing items | 0.000016 |
| closing tables | 0.000017 |
| logging slow query | 0.000006 |
+------------------------+-----------+

 
每行都是状态变化的过程以及它们持续的时间。Status那一列和SHOW FULL PROCESSLIST的State应该是一致的。
这个值是来自于thd->proc_info变量。因此你所查看的这个值是直接来自MySQL内部的。尽管这些数值是比较直接易懂的，你也可以查看MySQL手册。
 
你可以给SHOW PROFILES指定一个Query_ID来查看指定的语句，还可以给输出添加新的列。如，查看用户和CPU使用。可以用如下命令。
 

mysql> SHOW PROFILE CPU FOR QUERY 1;

 
SHOW PROFILE可以深入的查看服务器执行语句的工作情况。以及也能帮助你理解执行语句消耗时间的情况。一些限制是它没有实现的功能，不能查看和剖析其他连接的语句，以及剖析时所引起的消耗。

SHOW PROFILES显示最近发给服务器的多条语句，条数根据会话变量profiling_history_size定义，默认是15，最大值为100。设为0等价于关闭分析功能。

SHOW PROFILE FOR QUERY n，这里的n就是对应SHOW PROFILES输出中的Query_ID。


例如：

mysql> show profiles;

+----------+-------------+---------------------------------------+
| Query_ID | Duration | Query     |
+----------+-------------+---------------------------------------+
| 1 | 0.00037700 | alter table table1 drop column c3 int |
| 2 | 70.37123800 | alter table table1 drop column c3 |
| 3 | 0.00124500 | show tables    |
| 4 | 0.00569800 | select * from table1 where id=2 |
| 5 | 0.00068500 | select count(1) from tables1  |
| 6 | 0.00197900 | select count(1) from table1  |
| 7 | 0.00105900 | alter table tables1 drop c1  |
| 8 | 0.00800200 | alter table table1 drop c1  |
+----------+-------------+---------------------------------------+
8 rows in set (0.00 sec)

 

mysql> SHOW PROFILE FOR QUERY 2; #查看alter table table1 drop column c3的分析

+------------------------------+-----------+
| Status   | Duration |
+------------------------------+-----------+
| starting   | 0.000183 |
| checking permissions  | 0.000057 |
| checking permissions  | 0.000059 |
| init    | 0.000060 |
| Opening tables  | 0.000071 |
| System lock   | 0.000062 |
| setup   | 0.000080 |
| creating table  | 0.005052 |
| After create   | 0.000220 |
| copy to tmp table  | 0.000244 |
| rename result table  | 70.364027 |
| end    | 0.000575 |
| Waiting for query cache lock | 0.000062 |
| end    | 0.000075 |
| query end   | 0.000057 |
| closing tables  | 0.000061 |
| freeing items  | 0.000080 |
| logging slow query  | 0.000056 |
| logging slow query  | 0.000098 |
| cleaning up   | 0.000059 |
+------------------------------+-----------+
20 rows in set (0.00 sec)

如果没有指定FOR QUERY，那么输出最近一条语句的信息。

LIMIT部分的用法与SELECT中LIMIT子句一致，不赘述。

type是可选的，取值范围可以如下：

例：

mysql> show profile cpu for query 2;

+------------------------------+-----------+----------+------------+
| Status   | Duration | CPU_user | CPU_system |
+------------------------------+-----------+----------+------------+
| starting   | 0.000183 | 0.000000 | 0.000000 |
| checking permissions  | 0.000057 | 0.000000 | 0.000000 |
| checking permissions  | 0.000059 | 0.000000 | 0.000000 |
| init    | 0.000060 | 0.000000 | 0.000000 |
| Opening tables  | 0.000071 | 0.000000 | 0.000000 |
| System lock   | 0.000062 | 0.000000 | 0.000000 |
| setup   | 0.000080 | 0.000000 | 0.001000 |
| creating table  | 0.005052 | 0.003000 | 0.001000 |
| After create   | 0.000220 | 0.000000 | 0.000000 |
| copy to tmp table  | 0.000244 | 0.000000 | 0.000000 |
| rename result table  | 70.364027 | 7.470864 | 41.612674 |
| end    | 0.000575 | 0.000000 | 0.001000 |
| Waiting for query cache lock | 0.000062 | 0.000000 | 0.000000 |
| end    | 0.000075 | 0.000000 | 0.000000 |
| query end   | 0.000057 | 0.000000 | 0.000000 |
| closing tables  | 0.000061 | 0.000000 | 0.000000 |
| freeing items  | 0.000080 | 0.000000 | 0.000000 |
| logging slow query  | 0.000056 | 0.000000 | 0.000000 |
| logging slow query  | 0.000098 | 0.000000 | 0.000000 |
| cleaning up   | 0.000059 | 0.000000 | 0.000000 |
+------------------------------+-----------+----------+------------+
20 rows in set (0.00 sec)

ps:
SHOW PROFILE ALL FOR QUERY 2;的信息还可以通过SELECT * FROM information_schema.profiling WHERE query_id = 2 ORDER BY seq;获取。

作用范围
这个命令只是在本会话内起作用，即无法分析本会话外的语句。

开启分析功能后，所有本会话中的语句都被分析（甚至包括执行错误的语句），除了SHOW PROFILE和SHOW PROFILES两句本身。

应用示例：使用SHOW PROFILE分析查询缓存命中的性能优势。

mysql> set profiling=1;

Query OK, 0 rows affected (0.00 sec)

 

mysql> select count(1) as cnt from tran_excution;

+-------+
| cnt |
+-------+
| 14225 |
+-------+
1 row in set (0.00 sec)

由于已经启用了查询缓存，相同查询（非分区表）可以直接在查询缓存中命中。

mysql> select count(1) as cnt from tran_excution;

我们仔细看下两个同样的语句的分析。

mysql> show profile source for query 1;

+--------------------------------+----------+-----------------------+---------------+-------------+
| Status    | Duration | Source_function | Source_file | Source_line |
+--------------------------------+----------+-----------------------+---------------+-------------+
| starting   | 0.000048 | NULL   | NULL  | NULL |
| Waiting for query cache lock | 0.000013 | try_lock  | sql_cache.cc |  454 |
| checking query cache for query | 0.000040 | send_result_to_client | sql_cache.cc | 1561 |
| checking permissions  | 0.000023 | check_access  | sql_parse.cc | 4751 |
| Opening tables   | 0.000040 | open_tables  | sql_base.cc | 4831 |
| System lock   | 0.000020 | mysql_lock_tables | lock.cc |  299 |
| Waiting for query cache lock | 0.000037 | try_lock  | sql_cache.cc |  454 |
| init    | 0.000020 | mysql_select  | sql_select.cc | 2579 |
| optimizing   | 0.000015 | optimize  | sql_select.cc |  865 |
| statistics   | 0.000017 | optimize  | sql_select.cc | 1056 |
| preparing   | 0.000016 | optimize  | sql_select.cc | 1078 |
| executing   | 0.000015 | exec   | sql_select.cc | 1836 |
| Sending data   | 0.003875 | exec   | sql_select.cc | 2380 |
| end    | 0.000018 | mysql_select  | sql_select.cc | 2615 |
| query end   | 0.000015 | mysql_execute_command | sql_parse.cc | 4440 |
| closing tables   | 0.000016 | mysql_execute_command | sql_parse.cc | 4492 |
| freeing items   | 0.000016 | mysql_parse  | sql_parse.cc | 5640 |
| Waiting for query cache lock | 0.000012 | try_lock  | sql_cache.cc |  454 |
| freeing items   | 0.000032 | NULL   | NULL  | NULL |
| Waiting for query cache lock | 0.000017 | try_lock  | sql_cache.cc |  454 |
| freeing items   | 0.000016 | NULL   | NULL  | NULL |
| storing result in query cache | 0.000017 | end_of_result  | sql_cache.cc | 1020 |
| logging slow query  | 0.000018 | log_slow_statement | sql_parse.cc | 1461 |
| logging slow query  | 0.000050 | log_slow_statement | sql_parse.cc | 1470 |
| cleaning up   | 0.000018 | dispatch_command | sql_parse.cc | 1417 |
+--------------------------------+----------+-----------------------+---------------+-------------+
25 rows in set (0.00 sec)

 

mysql> show profile source for query 2;

+--------------------------------+----------+-----------------------+--------------+-------------+
| Status    | Duration | Source_function | Source_file | Source_line |
+--------------------------------+----------+-----------------------+--------------+-------------+
| starting   | 0.000051 | NULL   | NULL  | NULL |
| Waiting for query cache lock | 0.000014 | try_lock  | sql_cache.cc |  454 |
| checking query cache for query | 0.000016 | send_result_to_client | sql_cache.cc | 1561 |
| checking privileges on cached | 0.000013 | send_result_to_client | sql_cache.cc | 1652 |
| checking permissions  | 0.000015 | check_access  | sql_parse.cc | 4751 |
| sending cached result to clien | 0.000036 | send_result_to_client | sql_cache.cc | 1749 |
| logging slow query  | 0.000017 | log_slow_statement | sql_parse.cc | 1461 |
| cleaning up   | 0.000018 | dispatch_command | sql_parse.cc | 1417 |
+--------------------------------+----------+-----------------------+--------------+-------------+
8 rows in set (0.00 sec)

可以清晰地看到缓存中命中时，大大节省了后台的开销。当然缓存的使用也需要根据各种场景（表的数据规模，更新频率等）考察使用，并不是启用缓存就一定能够提高查询效率。这里仅仅作为SHOW PROFILE的一个应用示例。

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