深入研究insert into select语句锁表故障（上）

故障描述

前几天，一个mysql数据库运维同事，在生产上用insert into select * from语句，在生产上备份了一张表，结果将备份表全表锁住了，业务影响了大约10分钟。
看到这个语句，我第一反应就是select语句也能锁表，可是生产上的故障，证明确实锁表了。所以，需要将insert into select * from获取锁的情况彻底研究明白。

故障复盘

创建模拟表和模拟记录

[root@localhost] 17:39:55 [testdb1]>show create table t_test_1\G;
*************************** 1. row ***************************Table: t_test_1
Create Table: CREATE TABLE `t_test_1` (`id` int(11) NOT NULL,`name` char(10) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
1 row in set (0.00 sec)[root@localhost] 17:40:30 [testdb1]>select * from t_test_1;
+----+-------+
| id | name  |
+----+-------+
|  1 | trest |
|  2 | e99e  |
|  3 | test  |
|  4 | fresd |
|  5 | fsfa  |
+----+-------+
5 rows in set (0.00 sec)[root@localhost] 17:40:17 [testdb1]>show create table t_test_2\G;
*************************** 1. row ***************************Table: t_test_2
Create Table: CREATE TABLE `t_test_2` (`id` int(11) NOT NULL,`name` char(10) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
1 row in set (0.00 sec)

模拟insert into select操作

[root@localhost] 17:41:32 [testdb1]>begin;
Query OK, 0 rows affected (0.00 sec)[root@localhost] 17:41:33 [testdb1]>insert into t_test_2 select * from t_test_1 where name like 'trest';
Query OK, 1 row affected (0.02 sec)
Records: 1  Duplicates: 0  Warnings: 0

获取innodb的lock信息

[root@localhost] 17:42:00 [(none)]>show engine innodb status\G;
TRANSACTIONS
------------
Trx id counter 182551
Purge done for trx's n:o < 182551 undo n:o < 0 state: running but idle
History list length 0
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 421524582451936, not started
0 lock struct(s), heap size 1136, 0 row lock(s)
---TRANSACTION 182546, ACTIVE 20 sec
3 lock struct(s), heap size 1136, 6 row lock(s), undo log entries 1
MySQL thread id 7, OS thread handle 140049254979328, query id 82 localhost root

从innodb引擎获取的lock信息，太少了，只能看到有3 lock struct(s)，6 row lock(s)，不清楚那表申请的锁，申请什么类型的锁，不知道这些信息，就研究不明白故障到底怎么发生的。

幸运的是，mysql数据库提供一个参数innodb_status_output_locks，可以打印更详细的lock信息。

启用innodb_status_output_locks参数

启用innodb_status_output_locks参数，默认是不开启，所以需要开启。

[root@localhost] 17:31:12 [(none)]>show variables like 'innodb_status_output_locks';
+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| innodb_status_output_locks | OFF   |
+----------------------------+-------+
1 row in set (0.00 sec)[root@localhost] 17:47:41 [(none)]>set global innodb_status_output_locks=on;
Query OK, 0 rows affected (0.00 sec)[root@localhost] 17:47:41 [(none)]>show variables like 'innodb_status_output_locks';
+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| innodb_status_output_locks | ON    |
+----------------------------+-------+
1 row in set (0.00 sec)

获取innodb的lock详细信息
下面是开启innodb_status_output_locks参数之后，获取的详细lock信息

[root@localhost] 17:48:28 [(none)]>show engine innodb status\G;
TRANSACTIONS
------------
Trx id counter 182552
Purge done for trx's n:o < 182551 undo n:o < 0 state: running but idle
History list length 0
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 421524582451936, not started
0 lock struct(s), heap size 1136, 0 row lock(s)
---TRANSACTION 182551, ACTIVE 5 sec
3 lock struct(s), heap size 1136, 6 row lock(s), undo log entries 1
MySQL thread id 11, OS thread handle 140049254979328, query id 100 localhost root
TABLE LOCK table `testdb1`.`t_test_1` trx id 182551 lock mode IS
RECORD LOCKS space id 97 page no 3 n bits 72 index PRIMARY of table `testdb1`.`t_test_1` trx id 182551 lock mode S
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 00: len 8; hex 73757072656d756d; asc supremum;;Record lock, heap no 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 00: len 4; hex 80000001; asc     ;;1: len 6; hex 00000002c710; asc       ;;2: len 7; hex af000000310110; asc     1  ;;3: len 10; hex 74726573742020202020; asc trest     ;;Record lock, heap no 3 PHYSICAL RECORD: n_fields 4; compact format; info bits 00: len 4; hex 80000002; asc     ;;1: len 6; hex 00000002c710; asc       ;;2: len 7; hex af00000031011c; asc     1  ;;3: len 10; hex 65393965202020202020; asc e99e      ;;Record lock, heap no 4 PHYSICAL RECORD: n_fields 4; compact format; info bits 00: len 4; hex 80000003; asc     ;;1: len 6; hex 00000002c710; asc       ;;2: len 7; hex af000000310128; asc     1 (;;3: len 10; hex 74657374202020202020; asc test      ;;Record lock, heap no 5 PHYSICAL RECORD: n_fields 4; compact format; info bits 00: len 4; hex 80000004; asc     ;;1: len 6; hex 00000002c710; asc       ;;2: len 7; hex af000000310134; asc     1 4;;3: len 10; hex 66726573642020202020; asc fresd     ;;Record lock, heap no 6 PHYSICAL RECORD: n_fields 4; compact format; info bits 00: len 4; hex 80000005; asc     ;;1: len 6; hex 00000002c710; asc       ;;2: len 7; hex af000000310140; asc     1 @;;3: len 10; hex 66736661202020202020; asc fsfa      ;;TABLE LOCK table `testdb1`.`t_test_2` trx id 182551 lock mode IX

从上面的信息，可以很清晰看到，t_test_1获取到IS锁，并且有5个Record lock信息，即锁了5条记录，而此表只有5条记录，所以锁全表。
TABLE LOCK table testdb1.t_test_1 trx id 182551 lock mode IS

锁全表解决方案

insert into t_test_2 select * from t_test_1 where name like ‘trest’;这个sql语句中，t_test_1表的name字段没有索引，索引走了全表扫描，如果在name字段创建索引呢，会有什么变化呢
创建索引

[root@localhost] 17:54:33 [testdb1]>alter table t_test_1 add index idx_t_test_1_name (name);
Query OK, 0 rows affected (0.24 sec)
Records: 0  Duplicates: 0  Warnings: 0[root@localhost] 17:54:52 [testdb1]>begin;
Query OK, 0 rows affected (0.00 sec)[root@localhost] 17:54:55 [testdb1]>insert into t_test_2 select * from t_test_1 where name like 'trest';
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

重新获取innodb的lock详细信息

TRANSACTIONS
------------
Trx id counter 182565
Purge done for trx's n:o < 182565 undo n:o < 0 state: running but idle
History list length 0
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 421524582451936, not started
0 lock struct(s), heap size 1136, 0 row lock(s)
---TRANSACTION 182560, ACTIVE 3 sec
3 lock struct(s), heap size 1136, 2 row lock(s), undo log entries 1
MySQL thread id 11, OS thread handle 140049254979328, query id 105 localhost root
TABLE LOCK table `testdb1`.`t_test_1` trx id 182560 lock mode IS
RECORD LOCKS space id 97 page no 4 n bits 72 index idx_t_test_1_name of table `testdb1`.`t_test_1` trx id 182560 lock mode S
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 00: len 8; hex 73757072656d756d; asc supremum;;Record lock, heap no 6 PHYSICAL RECORD: n_fields 2; compact format; info bits 00: len 10; hex 74726573742020202020; asc trest     ;;1: len 4; hex 80000001; asc     ;;TABLE LOCK table `testdb1`.`t_test_2` trx id 182560 lock mode IX

看到没有，在这里，现在只有一个Record lock，不再是锁全表了。

深入研究insert into select锁表故障（下）

“深入研究insert into select语句锁表故障（上）”中，已经详细介绍了如何模拟insert into select锁表复盘，以及获取详细的Lock信息，和解决方案。

隔离级别
分析一个故障，一定要看数据库的隔离级别，在不同的隔离级别下，会有不一样的结果。

RR隔离级别
获取数据库的隔离级别

[root@localhost] 18:11:29 [testdb1]>show variables like '%iso%';
+-----------------------+-----------------+
| Variable_name         | Value           |
+-----------------------+-----------------+
| transaction_isolation | REPEATABLE-READ |
| tx_isolation          | REPEATABLE-READ |
+-----------------------+-----------------+
2 rows in set (0.00 sec)`

模拟insert into select锁表

[root@localhost] 17:54:52 [testdb1]>begin;
Query OK, 0 rows affected (0.00 sec)[root@localhost] 17:54:55 [testdb1]>insert into t_test_2 select * from t_test_1 where name like 'trest';
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

获取lock信息

TRANSACTIONS
------------
Trx id counter 182565
Purge done for trx's n:o < 182565 undo n:o < 0 state: running but idle
History list length 0
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 421524582451936, not started
0 lock struct(s), heap size 1136, 0 row lock(s)
---TRANSACTION 182560, ACTIVE 3 sec
3 lock struct(s), heap size 1136, 2 row lock(s), undo log entries 1
MySQL thread id 11, OS thread handle 140049254979328, query id 105 localhost root
TABLE LOCK table `testdb1`.`t_test_1` trx id 182560 lock mode IS
RECORD LOCKS space id 97 page no 4 n bits 72 index idx_t_test_1_name of table `testdb1`.`t_test_1` trx id 182560 lock mode S
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 00: len 8; hex 73757072656d756d; asc supremum;;Record lock, heap no 6 PHYSICAL RECORD: n_fields 2; compact format; info bits 00: len 10; hex 74726573742020202020; asc trest     ;;1: len 4; hex 80000001; asc     ;;TABLE LOCK table `testdb1`.`t_test_2` trx id 182560 lock mode IX

RC隔离级别
获取数据库的隔离级别

[root@localhost] 18:14:58 [(none)]>show variables like '%iso%';
+-----------------------+----------------+
| Variable_name         | Value          |
+-----------------------+----------------+
| transaction_isolation | READ-COMMITTED |
| tx_isolation          | READ-COMMITTED |
+-----------------------+----------------+
2 rows in set (0.00 sec)

获取lock信息

[root@localhost] 18:15:39 [(none)]>show engine innodb status\G;
TRANSACTIONS
------------
Trx id counter 183051
Purge done for trx's n:o < 183046 undo n:o < 0 state: running but idle
History list length 0
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 421137823890144, not started
0 lock struct(s), heap size 1136, 0 row lock(s)
---TRANSACTION 183050, ACTIVE 5 sec
1 lock struct(s), heap size 1136, 0 row lock(s), undo log entries 1
MySQL thread id 5, OS thread handle 139662496147200, query id 17 localhost root
TABLE LOCK table `testdb1`.`t_test_2` trx id 183050 lock mode IX

看到没有，在隔离级别RC下，insert into t_test_2 select * from t_test_1 where name like 'trest’语句，在t_test_1表上没有任何的lock产生。

建议

在生产使用insert into t_test_2 select * from t_test_1 where name like 'trest’语句时，有以下2个建议
建议一：建议mysql数据库隔离级别使用RC
建议二：select表的查询条件字段，建议创建索引

参考链接：

深入研究insert into select语句锁表故障（上） : https://mp.weixin.qq.com/s/PL0pIIfzYKJWq6qg7A1Hzw

深入研究insert into select锁表故障（下） : https://mp.weixin.qq.com/s/XpDPa8QlnqnpEoif2G40EQ

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