MySQL "set unique_checks", "set foreign_key_checks" vs. "alter table disable keys"

Question

We're having a problem where a mysqldump script is spending 90% of it's time populating a small handful of the tables it deals with. Eliminating FK's and indexes eliminates the speed problem, but is not an acceptable solution.

The dump script DOES have:

/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;

Can we expect any different behavior from "ALTER TABLE foo DISABLE KEYS"?

Also, being an alter table statement, is "disable keys" permanent until I re-enable? i.e., can I disable keys from one mysql session and have it effect the import issued from another session? Or is it a session-scoped statement?

Answer 1

Yes, you should get significant benefits out of DISABLE KEYS. It isn't session-scoped, it's a table property, so your keys will be dead for everybody until you do ENABLE KEYS.