Does a transaction lock the table MySQL?
1 Answer. A single statement like that works the same with MyISAM or InnoDB, with a transaction or with autocommit=ON. InnoDB locks only rows, not tables. (OK, DDL statement do bolder locks.)
What is optimistic locking in MySQL?
The OPTIMISTIC LOCKING way is: Note that the key point is in the structure of the UPDATE instruction and the subsequent number of affected rows check. It is these two things together that let your code realize that someone has already modified the data in between when you have executed the SELECT and UPDATE.
How does a transaction work in MySQL SQL?
A transaction is a way for you to execute one or more SQL statements as a single unit of work so that either all or none of the statements succeed. This appears to happen in isolation of work being done by any other transaction. If all the statements succeed, you commit the transaction to record their effect permanently in the database.
Why does MySQL maintain locks on every row?
MySQL must maintain locks on every row it updates until the transaction commits so it can roll them all back at once if the transaction fails or is cancelled. #As this is happening in transaction , mysql automatically applies lock on the concerned row. #waiting for the lock acquired by connection1 on the same row.
What does exclusive ( X ) lock in MySQL mean?
Exclusive (X) locks: It permits a transaction to update or delete a row. If transaction of one session has got this lock, no transaction of some other session can apply S or X lock on the same row. In a simple way we can say that other session can’t update that row but it can only read that row without asking for any lock.
Can you lock a table in share mode?
LOCK IN SHARE MODE inside a transaction, as you said, since normally SELECTs, no matter whether they are in a transaction or not, will not lock a table. Which one you choose would depend on whether you want other transactions to be able to read that row while your transaction is in progress.