Currently it is impossible to totally disable wait_timeout from disconnecting an idle client. wait_timeout being set to 0 should disable the idle timeout. Currently setting it to 0 will instead set it to 1 second, which makes idle connections disconnected after one second. No one would use this setting, so it shouldn't break backwards compatibility to add this feature. This is very useful when dealing with software which has a connection pool, since idle clients are expected. By having them disconnected every so often, it makes you lose the advantage of connection pooling in the first place.