删除查询 Mysql 5.7.18 中的锁定问题

Question

mysql 5.7.18 中删除查询中面临锁定问题。Mysql 版本 - 5.7.18 隔离级别 - READ-COMMITTED

Table structure:
mysql> show create table test;
+-------+---------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------+
| test  | CREATE TABLE `test` (
  `id` bigint(19) NOT NULL,
  `name` varchar(255) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

mysql> select * from test;
+----+------+
| id | name |
+----+------+
| 10 | a    |
+----+------+
1 row in set (0.00 sec)

问题：

交易1：

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

mysql> explain delete from test where id=10;
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key     | key_len | ref   | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------------+
|  1 | DELETE      | test  | NULL       | range | PRIMARY       | PRIMARY | 8       | const |    1 |   100.00 | Using where |
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------------+
1 row in set (0.00 sec)

mysql> delete from test where id=10;
Query OK, 1 row affected (0.00 sec)

交易2：

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

mysql> explain delete from test where id>1 and id<9;
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key     | key_len | ref   | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------------+
|  1 | DELETE      | test  | NULL       | range | PRIMARY       | PRIMARY | 8       | const |    1 |   100.00 | Using where |
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------------+
1 row in set (0.00 sec)

mysql> delete from test where id>1 and id<9;

查询正在等待锁定

更多细节：

mysql> select * from INFORMATION_SCHEMA.INNODB_TRX;
+---------+-----------+---------------------+-----------------------+---------------------+------------+---------------------+--------------------------------------+---------------------+-------------------+-------------------+------------------+-----------------------+-----------------+-------------------+-------------------------+---------------------+-------------------+------------------------+----------------------------+---------------------------+---------------------------+------------------+----------------------------+
| trx_id  | trx_state | trx_started         | trx_requested_lock_id | trx_wait_started    | trx_weight | trx_mysql_thread_id | trx_query                            | trx_operation_state | trx_tables_in_use | trx_tables_locked | trx_lock_structs | trx_lock_memory_bytes | trx_rows_locked | trx_rows_modified | trx_concurrency_tickets | trx_isolation_level | trx_unique_checks | trx_foreign_key_checks | trx_last_foreign_key_error | trx_adaptive_hash_latched | trx_adaptive_hash_timeout | trx_is_read_only | trx_autocommit_non_locking |
+---------+-----------+---------------------+-----------------------+---------------------+------------+---------------------+--------------------------------------+---------------------+-------------------+-------------------+------------------+-----------------------+-----------------+-------------------+-------------------------+---------------------+-------------------+------------------------+----------------------------+---------------------------+---------------------------+------------------+----------------------------+
| 6643991 | LOCK WAIT | 2022-05-09 19:00:57 | 6643991:2140:3:2      | 2022-05-09 19:01:51 |          2 |                   3 | delete from test where id>1 and id<9 | starting index read |                 1 |                 1 |                2 |                  1136 |               2 |                 0 |                       0 | REPEATABLE READ     |                 1 |                      1 | NULL                       |                         0 |                         0 |                0 |                          0 |
| 6643990 | RUNNING   | 2022-05-09 19:00:20 | NULL                  | NULL                |          3 |                   4 | NULL                                 | NULL                |                 0 |                 1 |                2 |                  1136 |               1 |                 1 |                       0 | READ COMMITTED      |                 1 |                      1 | NULL                       |                         0 |                         0 |                0 |                          0 |
+---------+-----------+---------------------+-----------------------+---------------------+------------+---------------------+--------------------------------------+---------------------+-------------------+-------------------+------------------+-----------------------+-----------------+-------------------+-------------------------+---------------------+-------------------+------------------------+----------------------------+---------------------------+---------------------------+------------------+----------------------------+
2 rows in set (0.01 sec)

mysql> select * from INFORMATION_SCHEMA.INNODB_LOCKS;
+------------------+-------------+-----------+-----------+--------------------+------------+------------+-----------+----------+-----------+
| lock_id          | lock_trx_id | lock_mode | lock_type | lock_table         | lock_index | lock_space | lock_page | lock_rec | lock_data |
+------------------+-------------+-----------+-----------+--------------------+------------+------------+-----------+----------+-----------+
| 6643991:2140:3:2 | 6643991     | X         | RECORD    | `testSchem`.`test` | PRIMARY    |       2140 |         3 |        2 | 10        |
| 6643990:2140:3:2 | 6643990     | X         | RECORD    | `testSchem`.`test` | PRIMARY    |       2140 |         3 |        2 | 10        |
+------------------+-------------+-----------+-----------+--------------------+------------+------------+-----------+----------+-----------+
2 rows in set, 1 warning (0.00 sec)

mysql> select * from INFORMATION_SCHEMA.INNODB_LOCK_WAITS;
+-------------------+-------------------+-----------------+------------------+
| requesting_trx_id | requested_lock_id | blocking_trx_id | blocking_lock_id |
+-------------------+-------------------+-----------------+------------------+
| 6643991           | 6643991:2140:3:2  | 6643990         | 6643990:2140:3:2 |
+-------------------+-------------------+-----------------+------------------+
1 row in set, 1 warning (0.00 sec)

mysql> select * from INFORMATION_SCHEMA.processlist;
+----+------+-----------+-----------+---------+------+-----------+----------------------------------------------+
| ID | USER | HOST      | DB        | COMMAND | TIME | STATE     | INFO                                         |
+----+------+-----------+-----------+---------+------+-----------+----------------------------------------------+
|  3 | root | localhost | testSchem | Query   |    2 | updating  | delete from test where id>1 and id<9         |
|  4 | root | localhost | testSchem | Sleep   |   93 |           | NULL                                         |
|  6 | root | localhost | NULL      | Query   |    0 | executing | select * from INFORMATION_SCHEMA.processlist |
+----+------+-----------+-----------+---------+------+-----------+----------------------------------------------+
3 rows in set (0.01 sec)

mysql> show engine innodb status;
+--------+------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Type   | Name | Status                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
+--------+------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| InnoDB |      | 
=====================================
2022-05-09 19:01:53 0x30af81000 INNODB MONITOR OUTPUT
=====================================
Per second averages calculated from the last 36 seconds
-----------------
BACKGROUND THREAD
-----------------
srv_master_thread loops: 10 srv_active, 0 srv_shutdown, 100253 srv_idle
srv_master_thread log flush and writes: 100261
----------
SEMAPHORES
----------
OS WAIT ARRAY INFO: reservation count 32
OS WAIT ARRAY INFO: signal count 29
RW-shared spins 0, rounds 28, OS waits 12
RW-excl spins 0, rounds 51, OS waits 0
RW-sx spins 0, rounds 0, OS waits 0
Spin rounds per wait: 28.00 RW-shared, 51.00 RW-excl, 0.00 RW-sx
------------
TRANSACTIONS
------------
Trx id counter 6643992
Purge done for trx's n:o < 6643990 undo n:o < 0 state: running but idle
History list length 6
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 4

    

Answer 1

这是间隙锁定的疯狂案例。

在开头只插入 id 10 是很奇怪的。间隙锁定基本上是在删除时锁定头部和尾部。它必须与您正在使用的 id 10 冲突。由于没有第 10 个编号列，MySQL 只是锁定本应出现的间隙。（这就是你的第三笔交易有效的原因。）

尝试将id 10更改为1；并使用：

First Transaction T1:

BEGIN;

DELETE FROM test WHERE id=1;


Second Transaction T2:

BEGIN;
DELETE FROM test WHERE id > 1 AND id<10;

我敢打赌它会起作用。让我知道你的想法。

*编辑

当我浏览此答案中的评论时，我正在答案中进行回复。

在我的用例和试验中，我发现这与删除查询和插入查询相矛盾。

考虑以下两笔交易：

First Transaction T1:

BEGIN;

SELECT * FROM `test` t WHERE t.`id`>1 AND t.`id`<10 FOR UPDATE;

Second Transaction T2:

BEGIN;

INSERT INTO test VALUES(5,'asgar');

首先尝试使用TRANSACTION ISOLATION LEVEL: READ_COMMITTED;

第二笔交易不停留GAP LOCK

但是，当我将其更改ISOLATION LEVEL为REPEATABLE READ：

SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;

并重新执行同一组交易，第二笔交易保留在GAP LOCK.

这些是在插入语句的情况下。然而，对于删除语句，隔离级别似乎并不影响。