剖析单条查询 profile:

mysql> show variables like '%prof%';
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| have_profiling         | YES   |
| profiling              | OFF   |
| profiling_history_size | 15    |
+------------------------+-------+
3 rows in set (0.00 sec)

mysql> set  profiling = 1;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> show variables like '%prof%';
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| have_profiling         | YES   |
| profiling              | ON    |
| profiling_history_size | 15    |
+------------------------+-------+
3 rows in set (0.00 sec)

mysql> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> select count(*) from user;
+----------+
| count(*) |
+----------+
|        4 |
+----------+
1 row in set (0.03 sec)

mysql> show profiles;
+----------+------------+------------------------------+
| Query_ID | Duration   | Query                        |
+----------+------------+------------------------------+
|        1 | 0.00103425 | show variables like '%prof%' |
|        2 | 0.00016325 | SELECT DATABASE()            |
|        3 | 0.00049450 | show databases               |
|        4 | 0.00039775 | show tables                  |
|        5 | 0.02702100 | select count(*) from user    |
+----------+------------+------------------------------+
5 rows in set, 1 warning (0.00 sec)

mysql> show profile for query 5;
+----------------------+----------+
| Status               | Duration |
+----------------------+----------+
| starting             | 0.000090 |
| checking permissions | 0.000012 |
| Opening tables       | 0.000030 |
| init                 | 0.000035 |
| System lock          | 0.000016 |
| optimizing           | 0.025417 |
| executing            | 0.000054 |
| end                  | 0.000551 |
| query end            | 0.000020 |
| closing tables       | 0.000021 |
| freeing items        | 0.000732 |
| cleaning up          | 0.000045 |
+----------------------+----------+
12 rows in set, 1 warning (0.00 sec)