keeping last 30 entries of a log table

I need to write a function which inserts a log entry in a log table and only
keeps the last 30 records. I was thinking of using a subquery similar to the
following:

insert into log (account_id, message) values (1, 'this is a test);
delete from log where account_id = 1 and id not in ( select id from log
where account_id = 1 order by timestamp desc limit 30);

I'm wondering if there is a more performance oriented method of doing the
delete that I'm not thinking of.

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Jeff Frost, Owner <jeff(at)frostconsultingllc(dot)com>
Frost Consulting, LLC http://www.frostconsultingllc.com/
Phone: 650-780-7908 FAX: 650-649-1954