mysql查询慢及如何解除死锁状态
查询慢的原因：1.数据量大 2.加索引及索引优化，explain查看是否命中索引 3.关联查询时，2张表的编码是否一致，具体见“mysql改变表编码及注意事项”
第一种：
前提条件：找到执行非常慢的sql；
如何找呢：还原客户遇到的问题场景，从控制台找到所执行的sql，一句句的去执行，直到找到执行非常慢的sql
1.查询是否锁表
show OPEN TABLES where In_use > 0;
2.查询进程（如果您有SUPER权限，您可以看到所有线程。否则，您只能看到您自己的线程）
show processlist
3.杀死conmand为waiting的进程id（就是上面命令的id列）
kill id
第二种：
1.查看下在锁的事务
SELECT * FROM INFORMATION_SCHEMA.INNODB_TRX;
2.杀死进程id（就是上面命令的trx_mysql_thread_id列）
kill 线程ID
第三种：
也许你无法查看到所在的info，这个时候你需要重启服务器，如果是分布式的话，就一台台重启吧；
原理是：杀死所有进程，释放所有锁。
MySQL - 锁等待超时与information_schema的三个表：
-- 1.information_schema.innodb_trx–当前运行的所有事务
select * from information_schema.innodb_trx;
-- information_schema.innodb_locks–当前出现的锁
select * from information_schema.innodb_locks;
-- information_schema.innodb_lock_waits–锁等待的对应关系
select * from information_schema.innodb_lock_waits;
-------------------------------------------------------------------------------------------
//常用
MySQL - 锁等待超时与information_schema的三个表：
-- 1.information_schema.innodb_trx–当前运行的所有事务
select * from information_schema.innodb_trx;
-- information_schema.innodb_locks–当前出现的锁
select * from information_schema.innodb_locks;
-- information_schema.innodb_lock_waits–锁等待的对应关系
select * from information_schema.innodb_lock_waits;
-------------------------------------------------------------------------------------------
//常用
select * from information_schema.innodb_trx where trx_state = 'LOCK WAIT';
SELECT a.* FROM information_schema.processlist a where command <> 'sleep' ORDER BY time desc
select * from information_schema.processlist where time> 60 and user='srapp_stsj';
SELECT
concat('kill',' ', id,';')
FROM
information_schema. PROCESSLIST a
WHERE
command <> 'sleep'
AND info LIKE 'select%'
AND time > 60
and user = 'srapp_stsj'
ORDER BY
time DESC
EXPLAIN
select * from sr_main where sys_scbj = '0' and mdjlx = 'ls_jz' and sys_spzt = 2
and mhzsfz = '330219193210200010'
----------------------------------------------------------------------------------------------------------------------------------------------
MySQL - 锁等待超时与information_schema的三个表：
-- 1.information_schema.innodb_trx–当前运行的所有事务
select *,trx_mysql_thread_id from information_schema.innodb_trx ;
-- information_schema.innodb_locks–当前出现的锁
select * from information_schema.innodb_locks;
-- information_schema.innodb_lock_waits–锁等待的对应关系
select * from information_schema.innodb_lock_waits;
-------------------------------------------------------------------------------------------
SELECT
trx_state,
trx_started,
trx_mysql_thread_id,
trx_query,
concat(
'kill ',
trx_mysql_thread_id,
';'
)
FROM
information_schema.innodb_trx
ORDER BY
trx_started -- limit 50
show processlist 看看有没有锁表
kill id
kill 34116988;kill 50403077; kill 50508905
-------------------------------------------------------------------------------------------
//常用
select * from information_schema.innodb_trx where trx_state = 'LOCK WAIT';
SELECT a.* FROM information_schema.processlist a where command <> 'sleep' ORDER BY time desc
select * from information_schema.processlist where time> 60 and user='srapp_stsj';
SELECT
concat('kill',' ', id,';')
FROM
information_schema. PROCESSLIST a
WHERE
command <> 'sleep'
AND info LIKE 'select%'
AND time > 60
and user = 'srapp_stsj'
ORDER BY
time DESC
----------------------------
SELECT
concat('kill',' ', id,';')
FROM
information_schema. PROCESSLIST a
WHERE
command <> 'sleep'
AND info LIKE 'select%'
AND time > 60
and user = 'srapp_stsj'
ORDER BY
time DESC
------------------------------
SELECT
*
FROM
information_schema. PROCESSLIST a
WHERE
command <> 'sleep'
AND info LIKE 'select%'
AND time > 60
and user = 'srapp_stsj'
ORDER BY
time DESC
EXPLAIN
select * from sr_main where sys_scbj = '0' and mdjlx = 'ls_jz' and sys_spzt = 2
and mhzsfz = '330219193210200010'
EXPLAIN
select 1 from sr_main where 1
---------------------------------------
SELECT
*
FROM
information_schema. PROCESSLIST a
WHERE
command <> 'sleep'
AND info LIKE 'select%'
AND time > 60
and user = 'srapp_stsj'
ORDER BY
time DESC
SELECT
concat('kill',' ', trx_mysql_thread_id,';')
FROM
information_schema.innodb_trx
