MySQL锁的调试
mysql> select version(); +-----------+ | version() | +-----------+ | 5.6.26 | +-----------+ 1 row in set (0.01 sec)
创建表，如下，
CREATE TABLE t (i INT) ENGINE = InnoDB; INSERT INTO t (i) VALUES(1);
client A，
mysql> START TRANSACTION; Query OK, 0 rows affected (0.00 sec) mysql> SELECT * FROM t WHERE i = 1 LOCK IN SHARE MODE; +------+ | i | +------+ | 1 | +------+ 1 row in set (0.00 sec)
Next, client B begins a transaction and attempts to delete the row from the table:
mysql> START TRANSACTION; Query OK, 0 rows affected (0.00 sec) mysql> DELETE FROM t WHERE i = 1;
The delete operation requires an X lock. The lock cannot be granted because it is incompatible with the S lock that client A holds, so the request goes on the queue of lock requests for the row and client B blocks.
此时，使用下面的sql可以显示谁阻塞和谁在等待，以及等待多久，
mysql> SELECT -> r.trx_id AS waiting_trx_id, r.trx_mysql_thread_id AS waiting_thread, TIMESTAMPDIFF(SECOND, r.trx_wait_started, CURRENT_TIMESTAMP) AS wait_time, r.trx_query AS waiting_query, l.lock_table AS waiting_table_lock, b.trx_id AS blocking_trx_id, b.trx_mysql_thread_id AS blocking_thread, IF(INSTR(p.host, ‘:‘) = 0, p.host, SUBSTRING(p.host, 1, INSTR(p.host, ‘:‘) - 1)) AS blocking_host, IF(INSTR(p.host, ‘:‘) = 0, ‘‘, SUBSTRING(p.host, INSTR(p.host, ‘:‘) + 1)) AS blocking_port, IF(p.command = ‘Sleep‘, p.time, 0) AS idle_in_trx, b.trx_query AS blocking_query FROM information_schema.innodb_lock_waits AS w INNER JOIN information_schema.innodb_trx AS b ON b.trx_id = w.blocking_trx_id INNER JOIN information_schema.INNODB_TRX AS r ON r.trx_id = w.requesting_trx_id INNER JOIN information_schema.INNODB_LOCKS AS l ON w.requested_l r.trx_id AS waiting_trx_id, -> r.trx_mysql_thread_id AS waiting_thread, -> TIMESTAMPDIFF(SECOND, -> r.trx_wait_started, -> CURRENT_TIMESTAMP) AS wait_time, -> r.trx_query AS waiting_query, -> l.lock_table AS waiting_table_lock, -> b.trx_id AS blocking_trx_id, -> b.trx_mysql_thread_id AS blocking_thread, -> IF(INSTR(p.host, ‘:‘) = 0, -> p.host, -> SUBSTRING(p.host, -> 1, -> INSTR(p.host, ‘:‘) - 1)) AS blocking_host, -> IF(INSTR(p.host, ‘:‘) = 0, -> ‘‘, -> SUBSTRING(p.host, -> INSTR(p.host, ‘:‘) + 1)) AS blocking_port, -> IF(p.command = ‘Sleep‘, p.time, 0) AS idle_in_trx, -> b.trx_query AS blocking_query -> FROM -> information_schema.innodb_lock_waits AS w -> INNER JOIN -> information_schema.innodb_trx AS b ON b.trx_id = w.blocking_trx_id -> INNER JOIN -> information_schema.INNODB_TRX AS r ON r.trx_id = w.requesting_trx_id -> INNER JOIN -> information_schema.INNODB_LOCKS AS l ON w.requested_lock_id = l.lock_id -> LEFT JOIN -> information_schema.PROCESSLIST AS p ON p.id = b.trx_mysql_thread_id -> ORDER BY wait_time DESC\G *************************** 1. row *************************** waiting_trx_id: 34106 waiting_thread: 4 wait_time: 1 waiting_query: DELETE FROM t WHERE i = 1 waiting_table_lock: `test`.`t` blocking_trx_id: 34105 blocking_thread: 1 blocking_host: localhost blocking_port: idle_in_trx: 1252 blocking_query: NULL 1 row in set (0.01 sec) mysql>
可以很清晰的看到事务34106正在等待，线程4正在等待，等待的时间为1秒。
还可以看到线程1导致了阻塞，其事务为34105，并且空闲了1252秒。
mysql> desc innodb_locks; +-------------+---------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------------+---------------------+------+-----+---------+-------+ | lock_id | varchar(81) | NO | | | | | lock_trx_id | varchar(18) | NO | | | | | lock_mode | varchar(32) | NO | | | | | lock_type | varchar(32) | NO | | | | | lock_table | varchar(1024) | NO | | | | | lock_index | varchar(1024) | YES | | NULL | | | lock_space | bigint(21) unsigned | YES | | NULL | | | lock_page | bigint(21) unsigned | YES | | NULL | | | lock_rec | bigint(21) unsigned | YES | | NULL | | | lock_data | varchar(8192) | YES | | NULL | | +-------------+---------------------+------+-----+---------+-------+
lock_id：锁 ID。
lock_trx_id：拥有锁的事务 ID。可以和 INNODB_TRX 表 JOIN 得到事务的详细信息。
lock_mode：锁的模式。有如下锁类型：行级锁包括：S、X、IS、IX，分别代表：共享锁、排它锁、意向共享锁、意向排它锁。表级锁包括：S_GAP、X_GAP、IS_GAP、IX_GAP 和 AUTO_INC，分别代表共享间隙锁、排它间隙锁、意向共享间隙锁、意向排它间隙锁和自动递增锁。
lock_type：锁的类型。RECORD 代表行级锁，TABLE 代表表级锁。
lock_table：被锁定的或者包含锁定记录的表的名称。
lock_index：当 LOCK_TYPE=’RECORD’ 时，表示索引的名称；否则为 NULL。
lock_space：当 LOCK_TYPE=’RECORD’ 时，表示锁定行的表空间 ID；否则为 NULL。
lock_page：当 LOCK_TYPE=’RECORD’ 时，表示锁定行的页号；否则为 NULL。
lock_rec：当 LOCK_TYPE=’RECORD’ 时，表示一堆页面中锁定行的数量，亦即被锁定的记录号；否则为 NULL。
lock_data：当 LOCK_TYPE=’RECORD’ 时，表示锁定行的主键；否则为NULL。
mysql> desc innodb_lock_waits; +-------------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------------------+-------------+------+-----+---------+-------+ | requesting_trx_id | varchar(18) | NO | | | | | requested_lock_id | varchar(81) | NO | | | | | blocking_trx_id | varchar(18) | NO | | | | | blocking_lock_id | varchar(81) | NO | | | | +-------------------+-------------+------+-----+---------+-------+
requesting_trx_id：请求事务的 ID。
requested_lock_id：事务所等待的锁定的 ID。可以和 INNODB_LOCKS 表 JOIN。
blocking_trx_id：阻塞事务的 ID。
blocking_lock_id：某一事务的锁的 ID，该事务阻塞了另一事务的运行。可以和 INNODB_LOCKS 表 JOIN。
mysql> desc innodb_trx; +----------------------------+---------------------+------+-----+---------------------+-------+ | Field | Type | Null | Key | Default | Extra | +----------------------------+---------------------+------+-----+---------------------+-------+ | trx_id | varchar(18) | NO | | | | | trx_state | varchar(13) | NO | | | | | trx_started | datetime | NO | | 0000-00-00 00:00:00 | | | trx_requested_lock_id | varchar(81) | YES | | NULL | | | trx_wait_started | datetime | YES | | NULL | | | trx_weight | bigint(21) unsigned | NO | | 0 | | | trx_mysql_thread_id | bigint(21) unsigned | NO | | 0 | | | trx_query | varchar(1024) | YES | | NULL | | | trx_operation_state | varchar(64) | YES | | NULL | | | trx_tables_in_use | bigint(21) unsigned | NO | | 0 | | | trx_tables_locked | bigint(21) unsigned | NO | | 0 | | | trx_lock_structs | bigint(21) unsigned | NO | | 0 | | | trx_lock_memory_bytes | bigint(21) unsigned | NO | | 0 | | | trx_rows_locked | bigint(21) unsigned | NO | | 0 | | | trx_rows_modified | bigint(21) unsigned | NO | | 0 | | | trx_concurrency_tickets | bigint(21) unsigned | NO | | 0 | | | trx_isolation_level | varchar(16) | NO | | | | | trx_unique_checks | int(1) | NO | | 0 | | | trx_foreign_key_checks | int(1) | NO | | 0 | | | trx_last_foreign_key_error | varchar(256) | YES | | NULL | | | trx_adaptive_hash_latched | int(1) | NO | | 0 | | | trx_adaptive_hash_timeout | bigint(21) unsigned | NO | | 0 | | | trx_is_read_only | int(1) | NO | | 0 | | | trx_autocommit_non_locking | int(1) | NO | | 0 | | +----------------------------+---------------------+------+-----+---------------------+-------+
trx_id：事务ID。
trx_state：事务状态，有以下几种状态：RUNNING、LOCK WAIT、ROLLING BACK 和 COMMITTING。
trx_started：事务开始时间。
trx_requested_lock_id：事务当前正在等待锁的标识，可以和 INNODB_LOCKS 表 JOIN 以得到更多详细信息。
trx_wait_started：事务开始等待的时间。
trx_weight：事务的权重。
trx_mysql_thread_id：事务线程 ID，可以和 PROCESSLIST 表 JOIN。
trx_query：事务正在执行的 SQL 语句。
trx_operation_state：事务当前操作状态。
trx_tables_in_use：当前事务执行的 SQL 中使用的表的个数。
trx_tables_locked：当前执行 SQL 的行锁数量。
trx_lock_structs：事务保留的锁数量。
trx_lock_memory_bytes：事务锁住的内存大小，单位为 BYTES。
trx_rows_locked：事务锁住的记录数。包含标记为 DELETED，并且已经保存到磁盘但对事务不可见的行。
trx_rows_modified：事务更改的行数。
trx_concurrency_tickets：事务并发票数。
trx_isolation_level：当前事务的隔离级别。
trx_unique_checks：是否打开唯一性检查的标识。
trx_foreign_key_checks：是否打开外键检查的标识。
trx_last_foreign_key_error：最后一次的外键错误信息。
trx_adaptive_hash_latched：自适应散列索引是否被当前事务锁住的标识。
trx_adaptive_hash_timeout：是否立刻放弃为自适应散列索引搜索 LATCH 的标识。
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原文：http://my.oschina.net/xinxingegeya/blog/530158