Database lock table? Don't panic, this article teaches you how to solve it

Reference resources ：https://zhuanlan.zhihu.com/p/437702115

Scenario and reason of locking table

scene

Locking tables usually occurs in DML（ insert 、update 、delete ） In the sentence , for example ： Program A Yes A Tabular a data Make changes , An error occurred during the modification , No, commit either rollback , This time the program B Yes A Tabular a Data modification , The resource is busy , That is, lock the watch .

DDL It will also cause table locking , For example, in MySql Operate a big watch , utilize alter Statement when modifying or adding fields , There happened to be a long affair （ Including reading ） When operating this table , Will trigger modification waiting , Cause lock table .

reason

When multiple transactions access multiple resources at the same time , If both parties have locked some resources but also need the locked resources of the other party , Unable to fully obtain the required resources in a limited time , Will be in an infinite waiting state , Thus causing the deadlock of resource demand , Cause the watch to lock .

How to unlock

Once the lock table is generated , We need to unlock it as soon as possible , Release resources , Otherwise it will be blocked all the time , Here is the main explanation MySql and Oracle How to unlock the database .

MySql Unlock

perform sql：

select * from information_schema.processlist where command not in ('Sleep') ORDER BY time desc

Through this sql You can find the following ：

sql The blocking duration has been sorted from large to small , Find records that take a long time id ,kill that will do ：

kill 123

You can also query mysql Slow sql sentence , To optimize ,info Fields are specifically executed sql sentence .

oracle Unlock （ See the original text of the reference link for details , It's not going to unfold here ）

How to avoid locking the table

Usually , Database lock table is mostly caused by unreasonable program design , When writing code , We should give full consideration to business scenarios , Try to achieve the following two points ：

1. Reduce... In the program DML（insert,update,delete） Time taken to operate , Isolate and control such operations , To prevent blocking .
2. If the transaction generates an exception , Ensure that the transaction can be rolled back normally .