On 2017-12-01 16:20:44 -0500, Robert Haas wrote: > Well, yeah, that would be insane. But I think even something very > rough could work well enough. I think our goal should be to eliminate > cache entries that are have gone unused for many *minutes*, and > there's no urgency about getting it to any sort of exact value. For > non-idle backends, using the most recent statement start time as a > proxy would probably be plenty good enough. Idle backends might need > a bit more thought.
Our timer framework is flexible enough that we can install a once-a-minute timer without much overhead. That timer could increment a 'cache generation' integer. Upon cache access we write the current generation into relcache / syscache (and potentially also plancache?) entries. Not entirely free, but cheap enough. In those once-a-minute passes entries that haven't been touched in X cycles get pruned. Greetings, Andres Freund
