From: Robert Haas [mailto:robertmh...@gmail.com] > I don't understand the idea that we would add something to PostgreSQL > without proving that it has value. Sure, other systems have somewhat > similar systems, and they have knobs to tune them. But, first, we > don't know that those other systems made all the right decisions, and > second, even they are, that doesn't mean that we'll derive similar > benefits in a system with a completely different code base and many > other internal differences.
I understand that general idea. So, I don't have an idea why the proposed approach, eviction based only on elapsed time only at hash table expansion, is better for PostgreSQL's code base and other internal differences... > You need to demonstrate that each and every GUC you propose to add has > a real, measurable benefit in some plausible scenario. You can't just > argue that other people have something kinda like this so we should > have it too. Or, well, you can argue that, but if you do, then -1 > from me. The benefit of the size limit are: * Controllable and predictable memory usage. The DBA can be sure that OOM won't happen. * Smoothed (non-abnormal) transaction response time. This is due to the elimination of bulk eviction of cache entries. I'm not sure how to tune catalog_cache_prune_min_age and catalog_cache_memory_target. Let me pick up a test scenario in a later mail in response to Horiguchi-san. Regards Takayuki Tsunakawa
