Does update lock the row?

Does update lock the row?

Typically no, but it depends (most often used answer for SQL Server!) SQL Server will have to lock the data involved in a transaction in some way. It has to lock the data in the table itself, and the data any affected indexes, while you perform a modification.

Can a select statement lock a table?

SELECT statements get a shared lock on the entire table. Other statements get exclusive locks on the entire table, which are released when the transaction commits. SELECT statements get shared locks on a range of rows. INSERT statements get exclusive locks on single rows (and sometimes on the preceding rows).

Is there any way to select without causing locking in MySQL?

As we know MyISAM can cause table level locks, especially if you have an update pending which will get locked, and then other select queries behind this update get locked too. So this method won’t prevent a lock, but it will make a lot of tiny locks, so as not to hang a website for example which needs a response within a very short frame of time.

How to improve insert into select in MySQL?

You can change READ-UNCOMMITTED to READ-COMMITTED which is a better isolation level. Everyone using Innodb tables probably got use to the fact Innodb tables perform non locking reads, meaning unless you use some modifiers such as LOCK IN SHARE MODE or FOR UPDATE, SELECT statements will not lock any rows while running.

Is there a way to select without locking in MyISAM?

MyISAM uses table locks to achieve a very high read speed, but if you have an UPDATE statement waiting, then future SELECTS will queue up behind the UPDATE. InnoDB tables use row-level locking, and you won’t have the whole table lock up behind an UPDATE.

How to improve insert into source table in MySQL?

In MySQL before 5.1 replication is statement based which means statements replied on the master should cause the same effect as on the slave. If Innodb would not locking rows in source table other transaction could modify the row and commit before transaction which is running INSERT .. SELECT statement.