On Tue, 15 Jan 2019 at 09:48, Tom Lane <t...@sss.pgh.pa.us> wrote: > > David Rowley <david.row...@2ndquadrant.com> writes: > > SELECT 1; I believe is a common query for some connection poolers as a > > sort of ping to the database. In light of that, the performance drop > > of 2 microseconds per query is not going to amount to very much in > > total for that use case. i.e you'll need to do half a million pings > > before it'll cost you 1 second of additional CPU time. > > Yeah, I agree this is not something to get hot & bothered over, but > I thought it was worth spending an hour seeing if there were any > easy wins. Not much luck.
Thanks for putting in the effort. > Anyway, herewith v6, rebased up to HEAD, with the build_simple_rel > improvement and the regression test fix I mentioned earlier. I had a look at these changes, I only have 1 comment: 1. I don't think having a table named "dual" makes a whole lot of sense for a table with a single row. I'm sure we can come up with a more suitably named table to serve the purpose. How about "single"? INSERT INTO J2_TBL VALUES (0, NULL); INSERT INTO J2_TBL VALUES (NULL, NULL); INSERT INTO J2_TBL VALUES (NULL, 0); +-- useful in some tests below +create temp table dual(); +insert into dual default values; +analyze dual; (Uppercasing these additions would also make them look less of an afterthought.) I also did a quick benchmark of v6 and found the slowdown to be smaller after the change made in build_simple_rel() Test 1 = explain select 1; Unpatched: $ pgbench -n -f bench.sql -T 60 postgres tps = 30259.096585 (excluding connections establishing) tps = 30094.533610 (excluding connections establishing) tps = 30124.154255 (excluding connections establishing) Patched: tps = 29667.414788 (excluding connections establishing) tps = 29555.325522 (excluding connections establishing) tps = 29101.083145 (excluding connections establishing) (2.38% down) Test 2 = select 1; Unpatched: tps = 36535.991023 (excluding connections establishing) tps = 36568.604011 (excluding connections establishing) tps = 35938.923066 (excluding connections establishing) Patched: tps = 35187.363260 (excluding connections establishing) tps = 35166.993210 (excluding connections establishing) tps = 35436.486315 (excluding connections establishing) (2.98% down) As far as I can see the patch is ready to go, but I'll defer to Mark, who's also listed on the reviewer list for this patch. -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
