查看事务锁：innodb_trx+innodb_locks+innodb_lock_waits

2021-08-09 06:54:53

当出现：ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction，要解决是一件麻烦的事情；特别是当一个SQL执行完了，但未COMMIT，后面的SQL想要执行就是被锁，超时结束，DBA光从数据库无法着手找出源头是哪个SQL锁住了；有时候看看 show engine innodb status，并结合 show full processlist 能暂时解决问题，但一直不能精确定位。

在5.5中，information_schema 库中增加了三个关于锁的表（MEMORY引擎）：
innodb_trx ## 当前运行的所有事务
innodb_locks ## 当前出现的锁
innodb_lock_waits ## 锁等待的对应关系

下面我们来动手看看数据吧：

##建立测试数据：
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use test;
create table tx1
(id int primary key ,
c1 varchar(20),
c2 varchar(30))
engine=innodb default charset = utf8 ;

insert into tx1 values
(1,’aaaa’,'aaaaa2′),
(2,’bbbb’,'bbbbb2′),
(3,’cccc’,'ccccc2′);

commit;
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###产生事务
### Session1
start transaction;
update tx1 set c1=’heyf’,c2=’heyf’ where id = 3;

### 产生事务，在 innodb_trx 就有数据
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root@127.0.0.1 : information_schema 13:38:21> select * from innodb_trx \G
*************************** 1. row ***************************
                    trx_id: 3669D82
                 trx_state: RUNNING
               trx_started: 2010-12-24 13:38:06
     trx_requested_lock_id: NULL
          trx_wait_started: NULL
                trx_weight: 3
       trx_mysql_thread_id: 2344
                 trx_query: NULL
       trx_operation_state: NULL
         trx_tables_in_use: 0
         trx_tables_locked: 0
          trx_lock_structs: 2
     trx_lock_memory_bytes: 376
           trx_rows_locked: 1
         trx_rows_modified: 1
   trx_concurrency_tickets: 0
       trx_isolation_level: REPEATABLE READ
         trx_unique_checks: 1
    trx_foreign_key_checks: 1
trx_last_foreign_key_error: NULL
trx_adaptive_hash_latched: 0
trx_adaptive_hash_timeout: 10000
1 row in set (0.00 sec)
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### 由于没有产生锁等待，下面两个表没有数据
root@127.0.0.1 : information_schema 13:38:31> select * from innodb_lock_waits \G
Empty set (0.00 sec)

root@127.0.0.1 : information_schema 13:38:57> select * from innodb_locks \G
Empty set (0.00 sec)

#### 产生锁等待
#### session 2
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start transaction;
update tx1 set c1=’heyfffff’,c2=’heyffffff’ where id =3 ;

root@127.0.0.1 : information_schema 13:39:01> select * from innodb_trx \G
*************************** 1. row ***************************
                    trx_id: 3669D83   ##第2个事务
                 trx_state: LOCK WAIT   ## 处于等待状态
               trx_started: 2010-12-24 13:40:07
     trx_requested_lock_id: 3669D83:49:3:4 ##请求的锁ID
          trx_wait_started: 2010-12-24 13:40:07
                trx_weight: 2
       trx_mysql_thread_id: 2346       ##线程 ID
                 trx_query: update tx1 set c1=’heyfffff’,c2=’heyffffff’ where id =3
       trx_operation_state: starting index read
         trx_tables_in_use: 1      ##需要用到1个表
         trx_tables_locked: 1      ##有1个表被锁
          trx_lock_structs: 2
     trx_lock_memory_bytes: 376
           trx_rows_locked: 1
         trx_rows_modified: 0
   trx_concurrency_tickets: 0
       trx_isolation_level: REPEATABLE READ
         trx_unique_checks: 1
    trx_foreign_key_checks: 1
trx_last_foreign_key_error: NULL
trx_adaptive_hash_latched: 0
trx_adaptive_hash_timeout: 10000
*************************** 2. row ***************************
                    trx_id: 3669D82 ##第1个事务
                 trx_state: RUNNING
               trx_started: 2010-12-24 13:38:06
     trx_requested_lock_id: NULL
          trx_wait_started: NULL
                trx_weight: 3
       trx_mysql_thread_id: 2344
                 trx_query: NULL
       trx_operation_state: NULL
         trx_tables_in_use: 0
         trx_tables_locked: 0
          trx_lock_structs: 2
     trx_lock_memory_bytes: 376
           trx_rows_locked: 1
         trx_rows_modified: 1
   trx_concurrency_tickets: 0
       trx_isolation_level: REPEATABLE READ
         trx_unique_checks: 1
    trx_foreign_key_checks: 1
trx_last_foreign_key_error: NULL
trx_adaptive_hash_latched: 0
trx_adaptive_hash_timeout: 10000
2 rows in set (0.00 sec)

root@127.0.0.1 : information_schema 13:40:12> select * from innodb_locks \G
*************************** 1. row ***************************
    lock_id: 3669D83:49:3:4      ## 第2个事务需要的锁
lock_trx_id: 3669D83
lock_mode: X
lock_type: RECORD
lock_table: `test`.`tx1`
lock_index: `PRIMARY`
lock_space: 49
lock_page: 3
   lock_rec: 4
lock_data: 3
*************************** 2. row ***************************
    lock_id: 3669D82:49:3:4     ## 第1个事务需要的锁
lock_trx_id: 3669D82
lock_mode: X
lock_type: RECORD
lock_table: `test`.`tx1`
lock_index: `PRIMARY`
lock_space: 49
lock_page: 3
   lock_rec: 4
lock_data: 3
2 rows in set (0.00 sec)

root@127.0.0.1 : information_schema 13:40:15> select * from innodb_lock_waits \G
*************************** 1. row ***************************
requesting_trx_id: 3669D83 ## 请求锁的事务
requested_lock_id: 3669D83:49:3:4 ## 请求锁的锁ID
blocking_trx_id: 3669D82 ## 拥有锁的事务
blocking_lock_id: 3669D82:49:3:4 ## 拥有锁的锁ID
1 row in set (0.00 sec)
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哈哈，有了以上这些信息，以下问题就迎刃而解啦。当前有哪些事务在等待锁？这些锁需要锁哪些表，锁哪些索引，锁哪些记录和值？处于等待状态的相关SQL是什么？在等待哪些事务完成？拥有当前锁的SQL是什么？

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