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.