Re: dbt2 performance regresses from 9.1.6 to 9.2.1 - Mailing list pgsql-performance

On Thu, Nov 1, 2012 at 12:51 AM, Dong Ye <yed@vmware.com> wrote:
> The average notpm is 61384.24 with 9.1.6 and 57381.43 with 9.2.1.
> Plotting notps over time shows that the slowdown of 9.2.1 is evident across the entire run period.
> Since we also observed sustained 80+% CPU utilization during both runs, we suspected this is a CPU bottleneck issue.
> So we run oprofile hoping that the profiles may suggest one is using CPU less productively than the other; but
nothingjumped out to that explanation. 
> The profiling results are posted on http://pgsql.privatepaste.com/3fa3ae0627 (9.1.6 run) and
http://pgsql.privatepaste.com/930bb51374(9.2.1 run). 

You are using prepared statements, this makes me think that this
regression might be due to support for parameter specific plans for
prepared statements. [1] Can you run the test on both versions without
prepared statements and see if the regressions remains.

I compared the profile results, I'll reproduce the results here incase
they ring any other bells for someone. Here are top 20 functions that
take more time under 9.2:

                                Function  Diff  v9.2%  v9.1%
                     postgres.copyObject  3.48 1.2436 0.3569
              postgres.check_stack_depth  1.92 0.7244 0.3774
 postgres.eval_const_expressions_mutator  1.87 0.3473 0.1853
                                jbd./jbd  1.82 0.4127 0.2271
              libc-2.14.1.so._int_malloc  1.75 1.4938 0.8540
           libc-2.14.1.so.__strlen_sse42  1.72 0.7098 0.4124
vmlinux-2.6.32.59-0.7-default.copy_user_generic_string  1.70 0.5130 0.3017
            postgres.MemoryContextCreate  1.68 0.3206 0.1914
  postgres.MemoryContextAllocZeroAligned  1.64 1.5443 0.9443
                libc-2.14.1.so._int_free  1.60 0.7182 0.4476
         postgres.expression_tree_walker  1.60 0.8350 0.5235
                     postgres.XLogInsert  1.58 2.7251 1.7210
                              ext3./ext3  1.55 0.2065 0.1335
           libc-2.14.1.so.__strcpy_ssse3  1.50 0.3061 0.2046
        postgres.expression_tree_mutator  1.41 0.3461 0.2447
      libc-2.14.1.so.__memcpy_ssse3_back  1.40 1.2379 0.8830
                  postgres.AllocSetAlloc  1.39 4.6567 3.3467
            postgres.LockAcquireExtended  1.39 0.2799 0.2015
             postgres.MemoryContextAlloc  1.38 1.0151 0.7373
                 postgres.AllocSetDelete  1.33 0.2130 0.1600

And top 10 functions present under 9.2 but not present with 9.1:
                              Function
              postgres._copyList.isra.15 0.341
       postgres._SPI_execute_plan.isra.4 0.224
               postgres.grouping_planner 0.220
                  postgres.IndexOnlyNext 0.213
                  postgres.GetCachedPlan 0.189
            postgres.MemoryContextStrdup 0.171
                      postgres.list_copy 0.165
              postgres.index_getnext_tid 0.155
         postgres.MemoryContextSetParent 0.128
          postgres.cost_qual_eval_walker 0.127

I have no idea why is XLogInsert taking so much longer on 9.2.

[1] http://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=e6faf910

Ants Aasma
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Cybertec Schönig & Schönig GmbH
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