On Tue, Jun 4, 2013 at 3:57 AM, Robert Haas <robertmh...@gmail.com> wrote:
> On Thu, May 30, 2013 at 1:39 AM, Michael Paquier > <michael.paqu...@gmail.com> wrote: > > +1. > > Here's a more serious patch for MVCC catalog access. This one > involves more data copying than the last one, I think, because the > previous version did not register the snapshots it took, which I think > is not safe. So this needs to be re-tested for performance, which I > have so far made no attempt to do. > > It strikes me as rather unfortunate that the snapshot interface is > designed in such a way as to require so much data copying. It seems > we always take a snapshot by copying from PGXACT/PGPROC into > CurrentSnapshotData or SecondarySnapshotData, and then copying data a > second time from there to someplace more permanent. It would be nice > to avoid that, at least in common cases. > And here are more results comparing master branch with and without this patch... 1) DDL CREATE/DROP test: 1-1) master: 250 connections: Create: 24846.060, Drop: 30391.713 Create: 23771.394, Drop: 29769.396 500 connections: Create: 24339.449, Drop: 30084.741 Create: 24152.176, Drop: 30643.471 1000 connections: Create: 26007.960, Drop: 31019.918 Create: 25937.592, Drop: 30600.341 2000 connections: Create: 26900.324, Drop: 30741.989 Create: 26910.660, Drop: 31577.247 1-2) mvcc catalogs: 250 connections: Create: 25371.342, Drop: 31458.952 Create: 25685.094, Drop: 31492.377 500 connections: Create: 28557.882, Drop: 33673.266 Create: 27901.910, Drop: 33223.006 1000 connections: Create: 31910.130, Drop: 36770.062 Create: 32210.093, Drop: 36754.888 2000 connections: Create: 40374.754, Drop: 43442.528 Create: 39763.691, Drop: 43234.243 2) backend startup 2-1) master branch: 250 connections: real 0m8.993s user 0m0.128s sys 0m0.380s 500 connections: real 0m9.004s user 0m0.212s sys 0m0.340s 1000 connections: real 0m9.072s user 0m0.272s sys 0m0.332s 2000 connections: real 0m9.257s user 0m0.204s sys 0m0.392s 2-2) MVCC catalogs: 250 connections: real 0m9.067s user 0m0.108s sys 0m0.396s 500 connections: real 0m9.034s user 0m0.112s sys 0m0.376s 1000 connections: real 0m9.303s user 0m0.176s sys 0m0.328s 2000 connections real 0m9.916s user 0m0.160s sys 0m0.428s Except for the case of backend startup test for 500 connections that looks to have some noise, performance degradation reaches 6% for 2000 connections, and less than 1% for 250 connections. This is better than last time. For the CREATE/DROP case, performance drop reaches 40% for 2000 connections (32% during last tests). I also noticed a lower performance drop for 250 connections now (3~4%) compared to the 1st time (9%). I compiled the main results on tables here: http://michael.otacoo.com/postgresql-2/postgres-9-4-devel-mvcc-catalog-access-take-2-2/ The results of last time are also available here: http://michael.otacoo.com/postgresql-2/postgres-9-4-devel-mvcc-catalog-access-2/ Regards, -- Michael
