Question

I am using Engine InnoDB on my MySQL server.

I have a patch script to upgrade my tables like add new columns and fill in default data.

I want to make sure there is no other session using the database. So I need a way to lock the database:

1. The lock shouldn’t kick out an existing session. If their is any other existing session just fail the lock and report error
2. The lock need to prevent other sessions to read/write/change the database.

Thanks a lot everyone!

Answer 1

You don’t need to worry about locking tables yourself. As the MySQL documentation (http://dev.mysql.com/doc/refman/5.1/en/alter-table.html) says:

In most cases, ALTER TABLE makes a temporary copy of the original
table. MySQL waits for other operations that are modifying the table,
then proceeds. It incorporates the alteration into the copy, deletes
the original table, and renames the new one. While ALTER TABLE is
executing, the original table is readable by other sessions. Updates
and writes to the table that begin after the ALTER TABLE operation
begins are stalled until the new table is ready, then are
automatically redirected to the new table without any failed updates.