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Do select queries lock tables MySQL?
SELECTs do not normally do any locking that you care about on InnoDB tables. The default transaction isolation level means that selects don’t lock stuff.
Does update query locks the table MySQL?
A locking read, an UPDATE , or a DELETE generally set record locks on every index record that is scanned in the processing of an SQL statement. It does not matter whether there are WHERE conditions in the statement that would exclude the row.
What is MySQL table lock?
A lock is a mechanism associated with a table used to restrict the unauthorized access of the data in a table. MySQL allows a client session to acquire a table lock explicitly to cooperate with other sessions to access the table’s data.
What happens when a table is locked in MySQL?
If another client issues LOCK TABLE t1 WRITE while the table remains locked, the client will block waiting for the lock, but the lock request causes In_use to be 2. If the count is zero, the table is open but not currently being used. In_use is also increased by the HANDLER
What does the lock flag mean in MySQL?
A lock is a flag associated with a table. MySQL allows a client session to explicitly acquire a table lock for preventing other sessions from accessing the same table during a specific period.
What are the features of a read lock in MySQL?
A READ lock has the following features: 1 A READ lock for a table can be acquired by multiple sessions at the same time. 2 The session that holds the READ lock can only read data from the table, but cannot write. 3 If the session is terminated, either normally or abnormally, MySQL will release all the locks implicitly.
How do you unlock a table in MySQL?
MySQL UNLOCK TABLES statement. To release a lock for a table, you use the following statement: UNLOCK TABLES; READ Locks. A READ lock has the following features: A READ lock for a table can be acquired by multiple sessions at the same time. In addition, other sessions can read data from the table without acquiring the lock.