Comment 8 for bug 1421471

Hmm, this bug says it's spending time doing the joins on the system_metadata table, but that should have been resolved with bug 1485025 and fix https://review.openstack.org/#/c/213340/ so that we're only loading up the instance_extra/flavor information, as the REST API code doesn't need system_metadata for the flavors (assuming you're instances have been migrated past kilo where flavors were moved out of the instance_system_metadata table and into instance_extra). That was fixed in liberty.