Solution to MySQL index not taking effect-Mysql Tutorial-php.cn

Solution to MySQL index not taking effect

黄舟

Release： 2017-09-19 11:03:04

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The mysql used by the company for services has been very slow recently when querying. It often takes more than 10 seconds. I checked the execution plan of the query and found that the index did not take effect.

The storage engine uses InnoDB.

When I first queried in the main database, I was always curious about why the index did not take effect. After switching to the standby database, I found that the standby database was effective.

I started to think about whether there was a problem with the index, and then rebuilt the index and found that the efficiency was much higher.

Simply record the comparison.

mysql> explain select * from runinfo where status in (0, 2, 1, 3, 4, 7, 9, 10);
+----+-------------+---------+-------+---------------+------+---------+------+----------+-------------+
| id | select_type | table   | type  | possible_keys | key  | key_len | ref  | rows     | Extra       |
+----+-------------+---------+-------+---------------+------+---------+------+----------+-------------+
|  1 | SIMPLE      | runinfo | All   | status_2      | NULL | NULL    | NULL |  2378055 | Using where |
+----+-------------+---------+-------+---------------+------+---------+------+----------+-------------+
row in set (0.00 sec)

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The above is the execution plan of the main library.

Compare the execution plan of the standby database.

mysql> explain select * from runinfo where status in (0, 2, 1, 3, 4, 7, 9, 10);
+----+-------------+---------+-------+---------------+----------+---------+------+------+-------------+
| id | select_type | table   | type  | possible_keys | key      | key_len | ref  | rows | Extra       |
+----+-------------+---------+-------+---------------+----------+---------+------+------+-------------+
|  1 | SIMPLE      | runinfo | range | status_2      | status_2 | 4       | NULL |  116 | Using where |
+----+-------------+---------+-------+---------------+----------+---------+------+------+-------------+
row in set (0.00 sec)

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It can be seen that the standby database adapts to index status_2 during query.

After executing the following command, the problem is solved.

mysql> OPTIMIZE TABLE runinfo;
+------------------+----------+----------+-------------------------------------------------------------------+
| Table            | Op       | Msg_type | Msg_text                                                          |
+------------------+----------+----------+-------------------------------------------------------------------+
| schedule.runinfo | optimize | note     | Table does not support optimize, doing recreate + analyze instead |
| schedule.runinfo | optimize | status   | OK                                                                |
+------------------+----------+----------+-------------------------------------------------------------------+
rows in set (47.13 sec)

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