Re: Finding bottleneck

From: Tom Lane
Subject: Re: Finding bottleneck
Date: ,
Msg-id: 15638.1124720273@sss.pgh.pa.us
(view: Whole thread, Raw)
In response to: Re: Finding bottleneck  ("Merlin Moncure")
List: pgsql-performance

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Finding bottleneck  (Kari Lavikka, )
 Re: Finding bottleneck  (Gavin Sherry, )
 Re: Finding bottleneck  (Claus Guttesen, )
 Re: Finding bottleneck  ("Merlin Moncure", )
 Re: Finding bottleneck  ("Luke Lonergan", )
  Re: Finding bottleneck  (Kari Lavikka, )
   Re: Finding bottleneck  (Tom Lane, )
 Re: Finding bottleneck  ("Merlin Moncure", )
  Re: Finding bottleneck  (Tom Lane, )
  Re: Finding bottleneck  (Kari Lavikka, )
   Re: Finding bottleneck  (Tom Lane, )
    Re: Finding bottleneck  (Kari Lavikka, )
     Re: Finding bottleneck  (Tom Lane, )
    Re: Finding bottleneck  (Kari Lavikka, )
     Re: Finding bottleneck  (Tom Lane, )
 Re: Finding bottleneck  (Ron, )
 Re: Finding bottleneck  ("Merlin Moncure", )
  Re: Finding bottleneck  (Tom Lane, )
 Re: Finding bottleneck  ("Merlin Moncure", )
 Re: Finding bottleneck  ("Merlin Moncure", )
  Re: Finding bottleneck  (Tom Lane, )
 Re: Finding bottleneck  ("Merlin Moncure", )

"Merlin Moncure" <> writes:
> One thing that might interest you is that the penalty in 8.1 for
> stats_command_string=true in this type of access pattern is very high: I
> was experimenting to see if the new cpu efficiency gave me enough of a
> budget to start using this.  This more than doubled the cpu load to
> around 70% with a runtime of 82 seconds.  This is actually worse than
> 8.0 :(.

That seems quite peculiar; AFAICS the pgstat code shouldn't be any
slower than before.  At first I thought it might be because we'd
increased PGSTAT_ACTIVITY_SIZE, but actually that happened before
8.0 release, so it shouldn't be a factor in this comparison.

Can anyone else confirm a larger penalty for stats_command_string in
HEAD than in 8.0?  A self-contained test case would be nice too.

            regards, tom lane


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