Contents
What causes a MySQL table lock?
Table locking causes problems when a session is waiting because the disk is full and free space needs to become available before the session can proceed. In this case, all sessions that want to access the problem table are also put in a waiting state until more disk space is made available.
What is waiting for table metadata lock in MySQL?
A metadata lock on a table prevents changes to the table’s structure. This locking approach has the implication that a table that is being used by a transaction within one session cannot be used in DDL statements by other sessions until the transaction ends.
Will select query lock the table in 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.
What causes waiting for table metadata lock?
A metadata lock wait may occur under the following scenarios: When you create or delete an index; When you modify the table structure; When you perform table maintenance operations (optimize table or repair table among others);
Does MySQL lock table on DELETE?
As for MySQL – it depends on the engine used For locking reads (SELECT with FOR UPDATE or FOR SHARE), UPDATE, and DELETE statements, the locks that are taken depend on whether the statement uses a unique index with a unique search condition, or a range-type search condition.
Does MySQL lock table on insert?
MySQL uses table locking (instead of row locking or column locking) on all table types, except InnoDB and BDB tables, to achieve a very high lock speed. Note that currently this only works if there are no holes after deleted rows in the table at the time the insert is made.
Why is MySQL waiting for table level lock?
At first glance, you want to do that on ID and username columns in the user table. Check the storage engine of the table .Change to Innodb if possible as it cause only row level locking. The queries which are running may be forcing a table lock even if you are using innodb tables if you are not using the index .
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.
Why do I get ” waiting for table metadata lock “?
My MySQL database serves three webapps as the storage backend. However I recently encounter permanantly the error “Waiting for table metadata lock”. It happen nearly all the time and I do not understand why. Of course one can kill the corresponding process.
How does a write lock work in MySQL?
A WRITE lock has the following features: The only session that holds the lock of a table can read and write data from the table. Other sessions cannot read data from and write data to the table until the WRITE lock is released. Let’s go into detail to see how the WRITE lock works.