Mysql innodb 锁定：当 X 被持有时，IX 不应该被授予，但是答案

【问题标题】：Mysql innodb locking: IX should not be granted when X is held, but doesMysql innodb 锁定：当 X 被持有时，IX 不应该被授予，但是
【发布时间】：2011-12-06 15:45:51
【问题描述】：

根据manual，IX 表锁与X 行锁冲突，因此在持有此类锁时无法授予。引用

如果与现有锁兼容，则将锁授予请求事务，但如果与现有锁冲突，则不会。

上表显示 IX 和 X 锁冲突。然而，这不是我所经历的。使用mysql命令行工具，如果我执行如下

drop table if exists test; create table test (A int, B int, primary key (A,B), index (A)) TYPE = InnoDB;  insert into test values (1,1); start transaction; delete from test where a=1;

然后运行 SHOW ENGINE INNODB STATUS，我得到了

------------
TRANSACTIONS
------------
Trx id counter 0 4604459
Purge done for trx's n:o < 0 4604457 undo n:o < 0 0
History list length 13
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 0 4604434, not started, process no 2015, OS thread id 140642069153536
MySQL thread id 55, query id 1689 localhost esben
---TRANSACTION 0 4604256, not started, process no 2015, OS thread id 140642068752128
MySQL thread id 45, query id 1708 localhost root
SHOW ENGINE INNODB STATUS
---TRANSACTION 0 4604458, ACTIVE 15 sec, process no 2015, OS thread id 140642068952832
2 lock struct(s), heap size 368, 2 row lock(s), undo log entries 1
MySQL thread id 56, query id 1707 localhost esben
TABLE LOCK table "esben_mosegris-esben-trunk"."test" trx id 0 4604458 lock mode IX
RECORD LOCKS space id 7800 page no 3 n bits 72 index "PRIMARY" of table "esben_mosegris-esben-trunk"."test" trx id 0 4604458 lock_mode X
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
 0: len 8; hex 73757072656d756d; asc supremum;;

Record lock, heap no 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
 0: len 4; hex 80000001; asc     ;; 1: len 4; hex 80000001; asc     ;; 2: len 6; hex 00000046422a; asc    FB*;; 3: len 7; hex 00000000392350; asc     9#P;;

请注意，事务 4604459 在表中的一个行上持有 X 锁，因此另一个事务应该不可能在“测试”表上获得 IX 锁。但是，执行

start transaction; delete from test where a=2;

在另一个mysql命令行客户端直接通过，给出如下输出

------------
TRANSACTIONS
------------
Trx id counter 0 4604460
Purge done for trx's n:o < 0 4604457 undo n:o < 0 0
History list length 13
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 0 4604256, not started, process no 2015, OS thread id 140642068752128
MySQL thread id 45, query id 1712 localhost root
SHOW ENGINE INNODB STATUS
---TRANSACTION 0 4604459, ACTIVE 18 sec, process no 2015, OS thread id 140642069153536
2 lock struct(s), heap size 368, 1 row lock(s)
MySQL thread id 55, query id 1710 localhost esben
TABLE LOCK table "esben_mosegris-esben-trunk"."test" trx id 0 4604459 lock mode IX
RECORD LOCKS space id 7800 page no 3 n bits 72 index "PRIMARY" of table "esben_mosegris-esben-trunk"."test" trx id 0 4604459 lock_mode X
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
 0: len 8; hex 73757072656d756d; asc supremum;;

---TRANSACTION 0 4604458, ACTIVE 55 sec, process no 2015, OS thread id 140642068952832
2 lock struct(s), heap size 368, 2 row lock(s), undo log entries 1
MySQL thread id 56, query id 1707 localhost esben
TABLE LOCK table "esben_mosegris-esben-trunk"."test" trx id 0 4604458 lock mode IX
RECORD LOCKS space id 7800 page no 3 n bits 72 index "PRIMARY" of table "esben_mosegris-esben-trunk"."test" trx id 0 4604458 lock_mode X
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
 0: len 8; hex 73757072656d756d; asc supremum;;

Record lock, heap no 2 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
 0: len 4; hex 80000001; asc     ;; 1: len 4; hex 80000001; asc     ;; 2: len 6; hex 00000046422a; asc    FB*;; 3: len 7; hex 00000000392350; asc     9#P;;

我错过了什么？我的问题是，因为这个位通过了，我进一步陷入僵局，因为两个事务现在都持有 IX 锁。或者可能是因为两者都试图获取相同的范围锁。我可以解决这个问题，但是我讨厌专门解决 mysql 怪异的代码，特别是当我无法解释时。

第二点，“记录锁定”中的所有这些字段是否在某处进行了解释？

【问题讨论】：

标签： mysql locking innodb

【解决方案1】：

我为此创建了一张票 http://bugs.mysql.com/bug.php?id=63665。原因是锁只在同一粒度上发生冲突，因此 ROW 锁永远不会与上表中的 TABLE 锁发生冲突。在票证中，我建议对手册进行一些改进，以使其更清晰。

【讨论】：