Table Locking Issues in MYSQL

by satheeshkumar 2012-09-18 21:27:01

Table Locking Issues in MYSQL ,

To achieve a very high lock speed, MySQL uses table locking (instead of page, row, or column locking) for all storage engines except InnoDB, BDB, and NDBCLUSTER.

For InnoDB and BDB tables, MySQL uses table locking only if you explicitly lock the table with LOCK TABLES. For these storage engines, avoid using LOCK TABLES at all, because InnoDB uses automatic row-level locking and BDB uses page-level locking to ensure transaction isolation.

For large tables, table locking is often better than row locking, but there are some disadvantages:

* Table locking enables many sessions to read from a table at the same time, but if a session wants to write to a table, it must first get exclusive access. During the update, all other sessions that want to access this particular table must wait until the update is done.

* Table locking causes problems in cases such as 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.

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