MySQL practice 45 lecture [row lock]

07 | The merits and demerits of line lock ： How to reduce the impact of row locks on performance ？

InnoDB It supports row locking .

Row locks are locks for row records in the data table . That makes sense , For example, affairs. A Updated a line , And at this time business B Also update the same line , Then we have to wait for business A You can't update until the operation of .

Start with two-stage locking

If you need to lock multiple rows in your transaction , The most likely cause of lock conflict 、 The lock most likely to affect concurrency should be put back as far as possible

Deadlock and deadlock detection
When different threads in a concurrent system have cyclic resource dependency , The threads involved are waiting for other threads to release resources , It will cause these threads to enter the state of infinite waiting , Deadlock . Here I use row locks in the database as an example .

--  Query transaction lock wait time , Unit second , Non interactive 
show variables like "innodb_lock_wait_timeout%"
set innodb_lock_wait_timeout=100;

innodb_lock_wait_timeout It refers to the maximum waiting time for a transaction to acquire resources ,
 If the resource is not allocated after this time, the application will fail 

--  Whether deadlock check is enabled 
show variables like "innodb_deadlock_detect%"

Summary

innodb Row level locking is achieved by locking index records .
If update No index ,innodb Inside, the whole table is scanned row by row according to the primary key index Lock line by line , The lock is released uniformly when the transaction is committed .