使用mysql profiling功能剖析单条查询
5.1版本开始引入show profile剖析单条语句功能，支持show profiles和show profile语句，参数have_profiling;控制是否开启：
查看是否支持这个功能（查询为yes表示支持）：
mysql > show variables like 'have_profiling';
+----------------+-------+
| Variable_name | Value |
+----------------+-------+
| have_profiling | YES |
+----------------+-------+
1 row in set (0.00 sec)
需要临时使用时直接sql命令行中输入：set profiling=1;来开启
mysql> set profiling=1;
Query OK, 0 rows affected, 1 warning (0.00 sec)
然后在服务器上执行SQL语句，都会被测量其消耗的时间和其他一些查询执行状态变更相关的数据
mysql> select count(*) from xx;
+----------+
| count(*) |
+----------+
| 262144 |
+----------+
1 row in set (0.05 sec)
然后再执行：show prifiles;命令，所有的查询SQL都会被列出来
mysql> show profiles;
+----------+------------+-------------------------+
| Query_ID | Duration | Query |
+----------+------------+-------------------------+
| 1 | 0.05645950 | select count(*) from xx |
+----------+------------+-------------------------+
1 row in set, 1 warning (0.00 sec)
然后根据编号查询具体SQL的执行过程，这里演示只执行了一句，那就选项query id为1
mysql> show profile for query 1;
+----------------------+----------+
| Status | Duration |
+----------------------+----------+
| starting | 0.000041 |
| checking permissions | 0.000004 |
| Opening tables | 0.000017 |
| init | 0.000010 |
| System lock | 0.000006 |
| optimizing | 0.000004 |
| statistics | 0.000009 |
| preparing | 0.000008 |
| executing | 0.000001 |
| Sending data | 0.056110 |
| end | 0.000009 |
| query end | 0.000007 |
| closing tables | 0.000011 |
| freeing items | 0.000121 |
| logging slow query | 0.000001 |
| logging slow query | 0.000093 |
| cleaning up | 0.000010 |
+----------------------+----------+
17 rows in set, 1 warning (0.00 sec)
当查到最耗时的线程状态时，可以进一步选择all或者cpu,block io,page faults等明细类型来查看mysql在每个线程状态中使用什么资源上耗费了过高的时间：
show profile cpu for query 2;
上面的输出中可以以很高的精度显示了查询的响应时间，列出了查询执行的每个步骤花费的时间，其结果很难确定哪个步骤花费的时间太多，因为输出是按照执行顺序排序，而不是按照花费大小来排序的，如果要按照花费大小排序，就不能使用show prifile命令，而是直接使用information_schema.profiling表。如：
mysql> set profiling=1;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> select count(*) from xx;
+----------+
| count(*) |
+----------+
| 262144 |
+----------+
1 row in set (0.05 sec)
mysql> show profiles;
+----------+------------+-------------------------+
| Query_ID | Duration | Query |
+----------+------------+-------------------------+
| 1 | 0.05509950 | select count(*) from xx |
+----------+------------+-------------------------+
1 row in set, 1 warning (0.00 sec)
mysql> set @query_id=1;
Query OK, 0 rows affected (0.00 sec)
mysql> select state,sum(duration) as total_r,round(100*sum(duration)/(select sum(duration) from information_schema.profiling where query_id=@query_id),2) as pct_r,count(*) as calls,sum(duration)/count(*) as "r/call" from information_schema.profiling where query_id=@query_id group by state order by total_r desc;
+----------------------+----------+-------+-------+--------------+
| state | total_r | pct_r | calls | r/call |
+----------------------+----------+-------+-------+--------------+
| Sending data | 0.054629 | 99.14 | 1 | 0.0546290000 |
| freeing items | 0.000267 | 0.48 | 1 | 0.0002670000 |
| logging slow query | 0.000070 | 0.13 | 2 | 0.0000350000 |
| starting | 0.000040 | 0.07 | 1 | 0.0000400000 |
| Opening tables | 0.000016 | 0.03 | 1 | 0.0000160000 |
| closing tables | 0.000011 | 0.02 | 1 | 0.0000110000 |
| init | 0.000010 | 0.02 | 1 | 0.0000100000 |
| cleaning up | 0.000010 | 0.02 | 1 | 0.0000100000 |
| end | 0.000009 | 0.02 | 1 | 0.0000090000 |
| statistics | 0.000009 | 0.02 | 1 | 0.0000090000 |
| preparing | 0.000008 | 0.01 | 1 | 0.0000080000 |
| query end | 0.000007 | 0.01 | 1 | 0.0000070000 |
| System lock | 0.000006 | 0.01 | 1 | 0.0000060000 |
| checking permissions | 0.000005 | 0.01 | 1 | 0.0000050000 |
| optimizing | 0.000004 | 0.01 | 1 | 0.0000040000 |
| executing | 0.000001 | 0.00 | 1 | 0.0000010000 |
+----------------------+----------+-------+-------+--------------+
16 rows in set (0.01 sec)
从上面的结果中可以看到，第一个是sending data（如果产生了临时表，第一就不是它了，那么临时表也是优先要解决的优化问题），另外还有sorting result（结果排序）也要注意，如果占比比较高，也要想办法优化，一般不建议在tuning sort buffer（优化排序缓冲区）或者类似的活动上花时间去优化。
如果要查询query id为1的Sending data状态的详细信息，可以使用如下SQL查询：
select * from information_schema.profiling where query_id=1 and state='Sending data'\G;
最后，做完剖析测试别忘记断开你的连接或者set profiling=0关闭这个功能。
