使用mysql profiles 来查看sql 语句执行计划

要使用该功能，mysql的版本必须在5.0.37版本以上。否则只能使用explain 的方式来检查。

profiling 功能可以了解到cpu io 等更详细的信息。

show profile 的格式如下：

SHOW PROFILE [type [, type] ... ]
    [FOR QUERY n]
    [LIMIT row_count [OFFSET offset]]

type:
    ALL
  | BLOCK IO
  | CONTEXT SWITCHES
  | CPU
  | IPC
  | MEMORY
  | PAGE FAULTS
  | SOURCE
  | SWAPS

默认方式下该功能是关闭的：

 mysql>select @@profiling;

+-------------+
| @@profiling |
+-------------+
|           0 |
+-------------+
1 row in set (0.00 sec)

打开功能

mysql>set profiling=1;

+-------------+
| @@profiling |
+-------------+
|           1 |
+-------------+
1 row in set (0.00 sec)

输入需要执行的sql 语句：

mysql>select count(*) from sysuser;

mysql>select count(*) from sysuser;

mysql> show profiles\G;
*************************** 1. row ***************************
Query_ID: 1
Duration: 0.00007550
   Query: select count(*) from sysuser
1 row in set (0.00 sec)

通过指定的Query_ID 来查询指定的sql语句的执行信息：

mysql> show profile for query 1;

+--------------------------------+----------+
| Status                         | Duration |
+--------------------------------+----------+
| starting                       | 0.000028 |
| checking query cache for query | 0.000008 |
| checking privileges on cached  | 0.000009 |
| sending cached result to clien | 0.000023 |
| logging slow query             | 0.000004 |
| cleaning up                    | 0.000003 |
+--------------------------------+----------+
6 rows in set (0.00 sec)

mysql> show profile cpu,block io for query 1;
+--------------------------------+----------+----------+------------+--------------+---------------+
| Status                         | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+--------------------------------+----------+----------+------------+--------------+---------------+
| starting                       | 0.000028 |     NULL |       NULL |         NULL |          NULL |
| checking query cache for query | 0.000008 |     NULL |       NULL |         NULL |          NULL |
| checking privileges on cached  | 0.000009 |     NULL |       NULL |         NULL |          NULL |
| sending cached result to clien | 0.000023 |     NULL |       NULL |         NULL |          NULL |
| logging slow query             | 0.000004 |     NULL |       NULL |         NULL |          NULL |
| cleaning up                    | 0.000003 |     NULL |       NULL |         NULL |          NULL |
+--------------------------------+----------+----------+------------+--------------+---------------+
6 rows in set (0.00 sec)

如果不带for 参数则指列出最后一条语句的profile 信息：

mysql> show profile cpu,block io for query 1;
+--------------------------------+----------+----------+------------+--------------+---------------+
| Status                         | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+--------------------------------+----------+----------+------------+--------------+---------------+
| starting                       | 0.000028 |     NULL |       NULL |         NULL |          NULL |
| checking query cache for query | 0.000008 |     NULL |       NULL |         NULL |          NULL |
| checking privileges on cached  | 0.000009 |     NULL |       NULL |         NULL |          NULL |
| sending cached result to clien | 0.000023 |     NULL |       NULL |         NULL |          NULL |
| logging slow query             | 0.000004 |     NULL |       NULL |         NULL |          NULL |
| cleaning up                    | 0.000003 |     NULL |       NULL |         NULL |          NULL |
+--------------------------------+----------+----------+------------+--------------+---------------+
6 rows in set (0.00 sec)

关闭参数：

mysql> set profiling=0

+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| profiling     | OFF   |
+---------------+-------+
1 row in set (0.00 sec)