On Mon, Jul 9, 2018 at 8:18 PM Peter Geoghegan <p...@bowt.ie> wrote: > On Mon, Jul 9, 2018 at 9:43 AM, Alexander Korotkov > <a.korot...@postgrespro.ru> wrote: > > In this case it also looks like we observed 1% regression. Despite 1% > > may seem to be very small, I think we should clarify whether it really > > exists. I have at least two hypothesis about this. > > > > 1) There is no real regression, observed difference of TPS is less > > than error of measurements. In order to check that we need to retry > > the experiment multiple times. Also, if you run benchmark on master > > before patched version (or vice versa) you should also try to swap the > > order to make sure there is no influence of the order of benchmarks. > > 2) If we consider relation between TPS and number of clients, TPS is > > typically growing with increasing number of clients until reach some > > saturation value. After the saturation value, there is some > > degradation of TPS. If patch makes some latency lower, that my cause > > saturation to happen earlier. In order to check that, we need run > > benchmarks with various number of clients and draw a graph: TPS > > depending on clients. > > > > So, may I ask you to make more experiments in order to clarify the > > observed regression? > > It would be nice to actually see script_duplicated.sql. I don't know > exactly what the test case was. > > Here is my wild guess: You may end up moving right more often within > _bt_findinsertloc(), which is actually worse than moving right within > _bt_moveright(), even when you _bt_moveright() in exclusive mode. > _bt_findinsertloc() couples/crabs exclusive buffer locks because the > unique case requires it, even when we're not inserting into a unique > index. Whereas _bt_moveright() holds at most one buffer lock at a > time.
I'm sorry, but I didn't understand this guess. I agree that moving right within _bt_findinsertloc() might be worse than moving right within _bt_moveright(). But why should it happen more often, if both with and without patch that happens only after _bt_moveright() in exclusive mode (with patch _bt_search() calls _bt_moveright() in exclusive mode)? ------ Alexander Korotkov Postgres Professional: http://www.postgrespro.com The Russian Postgres Company
