Unlock Table Release For Free

Answer: The only way to release a lock on an Oracle table is to kill the session that is holding the lock, or wait for the transaction to complete. See my related notes on finding Oracle locked_objects and killing_Oracle sessions.

To change the lock mode of a table in a database that was created without transaction logging, use the UNLOCK TABLE statement to unlock the table, then issue a new LOCK TABLE statement.

The correct way to use LOCK TABLES and UNLOCK TABLES with transactional tables, such as InnoDB tables, is to begin a transaction with SET autocommit = 0 (not START TRANSACTION ) followed by LOCK TABLES , and to not call UNLOCK TABLES until you commit the transaction explicitly.

To change the schema without locking a table, make sure that the original table contains a primary key or unique index. This allows you to copy all or part of data from the original table and synchronize incremental data. If the table contains only a primary key, make sure that the primary key is not updated.

In MySQL, locked tables are identified using the SHOW OPEN TABLES command. In its simplest form is displays all locked tables. All open tables in the table cache are listed, but the IN_USE column indicates of the table is locked. When the first lock is taken, the value increments to 1.

When a deletion query using a WHERE clause starts, it will lock that table. All other queries that are run against the table will have to wait. Because of the massive size of the table, the deletion query would probably run for hours. The lock would be in place for hours, essentially halting the entire app.

A session releases all the tables locks with it at once. You can implicitly release the table locks. If the connection to the server terminates explicitly or implicitly all the locks will be released. You can release the locks of a table explicitly using the UNLOCK TABLES statement.