Mysql alter table lock

Online DDL to InnoDB which speeds up and improves many things such as altering tables and indexes. Adding a column to a table will no longer require table locks except possibly brief exclusive locks at the start and end of the operation. ALTER TABLE permits them only as partitioning options, an as of MySQL 5. Create an index on a huge MySQL production table. You can safely use KILL to terminate a session that is waiting for a table lock.

LOCK TABLES and UNLOCK TABLES cannot be used within stored programs.

If your statements refer to a table by means of an alias, you must lock the table using that same alias. To use ALTER DATABASE, you need the ALTER privilege on the database. ALTER SCHEMA is a synonym for ALTER DATABASE.

The database name can be omitted from the first syntax, in which case the statement applies to the default database. National Language Characteristics. The CHARACTER SET clause changes the default database character set. When I alter MySQL table , add new column for my log table. But i still did not understand the fact why does the alter query take 60mins to add two columns when i run the Alter statement above.

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I am using MySQL Server version: 5. I need to add new null column. In order to avoid this MySQL 5. Previously, modifying the table while an index is being created or dropped typically resulted in a deadlock that cancelled the INSERT, UPDATE, or DELETE statement on the table. Summary: in this tutorial, you will learn how to use MySQL locking for cooperating table accesses between sessions. 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.

Here are some observations which hopefully could help narrow this down. SWITCH operation, the lock is acquired on both the source and target tables. A metadata lock is an implicit (from the user perspective) lock that prevents DDL against the table because something else needs the table to remain in its current form. This could happen if one connection first acquired a MDL_SHARED_READ lock on a table. ACCOUNT LOCK statements to lock user accounts in MySQL server.

To lock a user account, you can use the CREATE USER. This policy ensures that table locking is deadlock-free. There are, however, other things one needs to be aware of with this schema.

If you are using a LOW_PRIORITY_WRITE lock for a table , this means only that MySQL will wait for this particular lock until there are no threads that want a READ lock.

EDIT: Apparently this evaluation was too pessimistic. An alter table command in MySQL is very expensive. It creates a new version of the table based on what the table should look like with the alter DDL, proceeds to copy all of the records over to the new table , and then will swap the new table with the original table and delete the old table.