The query run by the ezkeywordlist operator can take up to 25 seconds when mysql is otherwise idle, and 500 seconds when load is higher. It is spending that time copying data to temp tables. The patch avoids this by elimination the ezcontentclass table from the query, instead it uses eZContentClass::classIDByIdentifier() to resolve the class ID before the query runs. This means one more query when class identifiers are not cached, but they usually are. The query now takes maximum 2-3 seconds in my tests, but usually close to zero.

The site has 32 000 content objects, 110 keywords, and 160 keyword assignments. Larger sites will benefit more.