Making changes to many tables at once

As an alternative to another recent blog post that answered the question “how can I truncate all the tables in my database,” I thought I’d show another way to do it, which does not use the INFORMATION_SCHEMA.

$ wget http://www.maatkit.org/get/mk-find
$ perl mk-find --exec 'TRUNCATE TABLE %D.%N'

The other example is how to alter MyISAM tables to be InnoDB. That one’s easy, too. Let’s alter all MyISAM tables in the ‘test’ database:

$ wget http://www.maatkit.org/get/mk-find
$ perl mk-find test --engine MyISAM --exec 'ALTER TABLE %D.%N ENGINE=InnoDB'

If you want to print out the commands instead of executing them, you can just use –printf instead of –exec.

Why would you do it this way instead of through the INFORMATION_SCHEMA database? I don’t think this can be said too often: querying the INFORMATION_SCHEMA database on MySQL can completely lock a busy server for a long time. It can even crash it. It is very dangerous. So whenever I mention it, I mention the dangers of using it. I use it too sometimes, but only when I know the server I’m working on.