1. 服务器级别的锁等待
通过show processlist看到等待锁的线程ID，但是无法知道究竟哪个线程持有锁？
通过mysqladmin debug
相关等待锁的线程及谁持有锁可以在错误日志中找到

2. 存储引擎层的锁等待则比较麻烦，以下是InnoDB存储引擎中锁等待以及哪个线程持有锁的查找SQL
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, SUBSTRING(p.host,1,INSTR(p.host, ':') -1 ) AS blocking_host, SUBSTRING(p.host, INSTR(p.host, ':') +1 ) AS block_port, IF(p.command="Sleep",p.time,0) AS idle_in_trx, b.trx_query AS blcoking_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

3. 如果因为线程在一个事务中空闲而正在遭受大量的锁操作，下面查询显示存储引擎层有多少查询被哪些线程阻塞？
SELECT CONCAT('thread ', b.trx_mysql_thread_id, ' from ',p.host) AS who_blocks, IF (p.command = "Sleep",p.time, 0) AS idle_in_trx, MAX(TIMESTAMPDIFF(SECOND,r.trx_wait_started,NOW())) AS max_wait_time, COUNT(*) AS num_waiters 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 left join information_schema.processlist as p on p.id = b.trx_mysql_thread_id group by who_blocks order by num_waiters desc\G
参考资料
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