在重构我的entries表并将source列拉入单独的sources表时，我正在执行更新，您可以在下面的slow_query_log中看到。
entries表的行数在2到3百万之间。
# Time: 120121 22:24:44
# User@Host: bt_user[bt_user] @ localhost []
# Query_time: 3910.984208 Lock_time: 0.091942 Rows_sent: 0 Rows_examined: 2092977602
SET timestamp=1327202684;
update entries set source_id = 4 where source = 'SOME_SOURCE';
另一个不好的案例：
mysql> update entries set source_id = 7 where source = 'SOME_OTHER_SOURCE';
Query OK, 31270 rows affected (53 min 3.37 sec)
Rows matched: 31270 Changed: 31270 Warnings: 0
# Time: 120121 23:43:36
# User@Host: root[root] @ localhost []
# Query_time: 3183.845250 Lock_time: 0.000110 Rows_sent: 0 Rows_examined: 875871174
SET timestamp=1327207416;
update entries set source_id = 7 where source = 'SOME_OTHER_SOURCE';
这是一个更正常的案例：
mysql> update entries set source_id = 6 where source = 'YET_ANOTHER_SOURCE';
Query OK, 138592 rows affected (23.84 sec)
Rows matched: 138592 Changed: 138592 Warnings: 0
# Time: 120121 22:49:54
# User@Host: root[root] @ localhost []
# Query_time: 23.843946 Lock_time: 0.000149 Rows_sent: 0 Rows_examined: 554368
SET timestamp=1327204194;
update entries set source_id = 6 where source = 'YET_ANOTHER_SOURCE';
知道非常大 Rows_examined 的交易是什么？如果我可以确定，我会理解为什么有问题的交易需要花费一个多小时来执行。
如果您需要更多信息，请询问，我会尽力提供。谢谢你的帮助！
mysql> show create table entries\G
*************************** 1. row ***************************
Table: entries
Create Table: CREATE TABLE `entries` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`source` varchar(100) NOT NULL,
`source_id` int(10) unsigned NOT NULL DEFAULT '1000',
`ip` int(10) unsigned DEFAULT NULL,
`domain` varchar(255) DEFAULT NULL,
`url` varchar(2038) DEFAULT NULL,
`info` varchar(255) DEFAULT NULL,
`md5` varchar(32) NOT NULL,
`start_date` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
`end_date` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
PRIMARY KEY (`id`),
KEY `both_date_source_index` (`start_date`,`end_date`,`source`),
KEY `source_index` (`source`),
KEY `ip_index` (`ip`),
KEY `domain_part_index` (`domain`(20)),
KEY `url_part_index` (`url`(30)),
KEY `md5_index` (`md5`)
) ENGINE=InnoDB AUTO_INCREMENT=2355472 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
索引可能需要一些审核，但如果这影响了我的问题......
我的触发器（可能有更好的方法）：
mysql> show triggers\G
*************************** 1. row ***************************
Trigger: after_insert_count
Event: INSERT
Table: entries
Statement: BEGIN
IF NEW.ip IS NOT NULL THEN
IF (SELECT COUNT(*) FROM ip_counts WHERE ip = NEW.ip) > 0 THEN
UPDATE ip_counts SET count = count+1 WHERE ip = NEW.ip;
ELSE
INSERT INTO ip_counts (ip, count) VALUES (NEW.ip, 1);
END IF;
END IF;
IF NEW.domain IS NOT NULL THEN
IF (SELECT COUNT(*) FROM domain_counts WHERE domain = NEW.domain) > 0 THEN
UPDATE domain_counts SET count = count+1 WHERE domain = NEW.domain;
ELSE
INSERT INTO domain_counts (domain, count) VALUES (NEW.domain, 1);
END IF;
END IF;
IF NEW.url IS NOT NULL THEN
IF (SELECT COUNT(*) FROM url_counts WHERE url = NEW.url) > 0 THEN
UPDATE url_counts SET count = count+1 WHERE url = NEW.url;
ELSE
INSERT INTO url_counts (url, count) VALUES (NEW.url, 1);
END IF;
END IF;
END
Timing: AFTER
Created: NULL
sql_mode:
Definer: root@localhost
character_set_client: utf8
collation_connection: utf8_general_ci
Database Collation: utf8_general_ci
*************************** 2. row ***************************
Trigger: after_update_count
Event: UPDATE
Table: entries
Statement: BEGIN
IF OLD.ip IS NOT NULL THEN
UPDATE ip_counts SET count = count-1 WHERE ip = OLD.ip;
END IF;
IF OLD.domain IS NOT NULL THEN
UPDATE domain_counts SET count = count-1 WHERE domain = OLD.domain;
END IF;
IF OLD.url IS NOT NULL THEN
UPDATE url_counts SET count = count-1 WHERE url = OLD.url;
END IF;
IF NEW.ip IS NOT NULL THEN
IF (SELECT COUNT(*) FROM ip_counts WHERE ip = NEW.ip) > 0 THEN
UPDATE ip_counts SET count = count+1 WHERE ip = NEW.ip;
ELSE
INSERT INTO ip_counts (ip, count) VALUES (NEW.ip, 1);
END IF;
END IF;
IF NEW.domain IS NOT NULL THEN
IF (SELECT COUNT(*) FROM domain_counts WHERE domain = NEW.domain) > 0 THEN
UPDATE domain_counts SET count = count+1 WHERE domain = NEW.domain;
ELSE
INSERT INTO domain_counts (domain, count) VALUES (NEW.domain, 1);
END IF;
END IF;
IF NEW.url IS NOT NULL THEN
IF (SELECT COUNT(*) FROM url_counts WHERE url = NEW.url) > 0 THEN
UPDATE url_counts SET count = count+1 WHERE url = NEW.url;
ELSE
INSERT INTO url_counts (url, count) VALUES (NEW.url, 1);
END IF;
END IF;
END
Timing: AFTER
Created: NULL
sql_mode:
Definer: root@localhost
character_set_client: utf8
collation_connection: utf8_general_ci
Database Collation: utf8_general_ci
*************************** 3. row ***************************
Trigger: after_delete_count
Event: DELETE
Table: entries
Statement: BEGIN
IF OLD.ip IS NOT NULL THEN
UPDATE ip_counts SET count = count-1 WHERE ip = OLD.ip;
END IF;
IF OLD.domain IS NOT NULL THEN
UPDATE domain_counts SET count = count-1 WHERE domain = OLD.domain;
END IF;
IF OLD.url IS NOT NULL THEN
UPDATE url_counts SET count = count-1 WHERE url = OLD.url;
END IF;
END
Timing: AFTER
Created: NULL
sql_mode:
Definer: root@localhost
character_set_client: utf8
collation_connection: utf8_general_ci
Database Collation: utf8_general_ci
3 rows in set (0.00 sec)
答案 0 :(得分：1)
使用更新时，插入或删除语句触发器可以响应极长的查询执行时间和slow_query_log文件中令人惊讶的高Rows_examined计数。
要查看表使用的所有触发器：
SHOW TRIGGERS WHERE `table`='tblName'
Mysql必须运行触发器块中的每个语句，通常会影响其他表，因此Rows_examined可以是任何内容，不一定与更新表的行数有关。
在您的情况下，在更新中受影响的每一行都会调用一个触发器来检查某些字段是否为NOT NULL，这并不意味着它们实际上已被更改，而只是检查是否存在非空值对于符合更新条件的给定行中的该列。