Запрос:
UPDATE `cart` SET `user_id` = NULL, `completed` = 0 WHERE `id` = 6948;
Query OK, 0 rows affected (1.21 sec)
Rows matched: 1 Changed: 0 Warnings: 0
Видно, что затронуто 0 строк, тем не менее 1210 мс - это шикарно. SELECT этой строки всегда за 0мс.
Размер таблицы (6,354 rows).
describe cart;
+-----------+------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| user_id | int(11) | YES | MUL | NULL | |
| completed | tinyint(1) | NO | | 0 | |
+-----------+------------+------+-----+---------+----------------+
3 rows in set (0.01 sec)
show index from cart;
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| cart | 0 | PRIMARY | 1 | id | A | 6386 | NULL | NULL | | BTREE | | |
| cart | 1 | user_id | 1 | user_id | A | 2128 | NULL | NULL | YES | BTREE | | |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
Вот кусок профилирования этого запроса который виновен:
| Status | Duration | CPU_user | CPU_system | Context_voluntary | Context_involuntary | Block_ops_in | Block_ops_out | Messages_sent | Messages_received | Page_faults_major | Page_faults_minor | Swaps | Source_function | Source_file | Source_line |
| query end | 2.502555 | 0.003000 | 0.000000 | 88 | 8 | 0| 136 | 0 | 0 | 0 | 0 | 0 | mysql_execute_command | sql_parse.cc | 5093 |
Server version: 10.0.17-MariaDB-1~wheezy
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