Mysql lock read

Mysql lock read
Locking Reads

In the same transaction, if you query data first and then insert or modify the relevant data, the standard SLELECT will not provide sufficient protection. During your query, another transaction can update or delete the same row. InnoDB provides two types of lock reads:

• SELECT... LOCK IN SHARE MODE

Add a shared lock to each row. Other sessions can also read these rows, but they cannot be modified until your transaction is committed. If these rows have been modified by other transactions but have not yet been committed, your query must wait until the transaction ends.

• SELECT... FOR UPDATE

For none of the retrieved index records, lock these rows and the associated index records

 

In fact, the former is an intention-sharing lock, and the latter is an intention-exclusive lock.