> On Jul 25, 2018, at 10:25 PM, Amit Kapila <amit.kapil...@gmail.com> wrote: > > On Wed, Jul 25, 2018 at 7:42 PM, Jonathan S. Katz > <jonathan.k...@excoventures.com> wrote: >> >> On Jul 7, 2018, at 12:03 AM, Amit Kapila <amit.kapil...@gmail.com> wrote: >> >> I tried running the below on both 11beta2 and HEAD with the patch >> applied: >> >> CREATE UNLOGGED TABLE t1 (c1 int); >> INSERT INTO t1 SELECT generate_series(1,100000000); >> /** restart PostgreSQL */ >> EXPLAIN (analyze,buffers,timing off,costs off) >> SELECT count(*) FROM t1; >> /** repeat above two queries */ >> >> I have identical postgresql.conf files on both instances as well. >> >> 11beta2 >> ====== >> buffers=# explain (analyze,buffers,timing off,costs off) select count(*) >> from t1; >> QUERY PLAN >> >> -------------------------------------------------------------------------- >> Finalize Aggregate (actual rows=1 loops=1) >> Buffers: shared read=63175 >> -> Gather (actual rows=7 loops=1) >> Workers Planned: 6 >> Workers Launched: 6 >> Buffers: shared read=63175 >> -> Partial Aggregate (actual rows=1 loops=7) >> Buffers: shared read=442478 >> -> Parallel Seq Scan on t1 (actual rows=14285714 >> loops=7) >> Buffers: shared read=442478 >> Planning Time: 1.422 ms >> Execution Time: 3214.407 ms >> (12 rows) >> >> buffers=# explain (analyze,buffers,timing off,costs off) select count(*) >> from t1; >> QUERY PLAN >> >> -------------------------------------------------------------------------- >> Finalize Aggregate (actual rows=1 loops=1) >> Buffers: shared hit=27 read=64960 >> -> Gather (actual rows=7 loops=1) >> Workers Planned: 6 >> Workers Launched: 6 >> Buffers: shared hit=27 read=64960 >> -> Partial Aggregate (actual rows=1 loops=7) >> Buffers: shared hit=224 read=442254 >> -> Parallel Seq Scan on t1 (actual rows=14285714 >> loops=7) >> Buffers: shared hit=224 read=442254 >> Planning Time: 0.080 ms >> Execution Time: 3774.091 ms >> (12 rows) >> >> HEAD >> ===== >> buffers=# explain (analyze,buffers,timing off,costs off) select count(*) >> from t1; >> QUERY PLAN >> >> -------------------------------------------------------------------------- >> Finalize Aggregate (actual rows=1 loops=1) >> Buffers: shared read=442478 >> -> Gather (actual rows=7 loops=1) >> Workers Planned: 6 >> Workers Launched: 6 >> Buffers: shared read=442478 >> -> Partial Aggregate (actual rows=1 loops=7) >> Buffers: shared read=442478 >> -> Parallel Seq Scan on t1 (actual rows=14285714 >> loops=7) >> Buffers: shared read=442478 >> Planning Time: 1.594 ms >> Execution Time: 6207.799 ms >> (12 rows) >> >> buffers=# explain (analyze,buffers,timing off,costs off) select count(*) >> from t1; >> QUERY PLAN >> >> -------------------------------------------------------------------------- >> Finalize Aggregate (actual rows=1 loops=1) >> Buffers: shared hit=224 read=442254 >> -> Gather (actual rows=7 loops=1) >> Workers Planned: 6 >> Workers Launched: 6 >> Buffers: shared hit=224 read=442254 >> -> Partial Aggregate (actual rows=1 loops=7) >> Buffers: shared hit=224 read=442254 >> -> Parallel Seq Scan on t1 (actual rows=14285714 >> loops=7) >> Buffers: shared hit=224 read=442254 >> Planning Time: 0.074 ms >> Execution Time: 5006.395 ms >> (12 rows) >> >> Notice the “read” numbers just before the “Finalize Aggregate” is much >> higher, >> > > You mean to say the number (Buffers: shared read=442478) in HEAD, > right? If so, yeah, I am also wondering why the results of the patch > are different in HEAD and 11beta2. So, if I read correctly, the > numbers in 11beta2 appears correct, but on HEAD it is not correct, it > should have divided the buffers read by loops. I will figure that > out, but this is just to clarify that both of us are seeing the > results in the same way.
I’ll try it again but patch it against 11beta2 and see what results I get. > >> and there appears to be a performance hit. >> > > Do you mean to say the performance of the same query in 11beta2 and > HEAD or something else? Correct. But per your advice let me try running it against a patched version of 11beta2 and see what happens. Jonathan
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