From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Michael Fuhr <mike(at)fuhr(dot)org> |
Cc: | Merlin Moncure <merlin(dot)moncure(at)rcsonline(dot)com>, pgsql-performance(at)postgresql(dot)org, Carlos Benkendorf <carlosbenkendorf(at)yahoo(dot)com(dot)br> |
Subject: | Re: How much expensive are row level statistics? |
Date: | 2005-12-13 03:20:45 |
Message-ID: | 1667.1134444045@sss.pgh.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers pgsql-patches pgsql-performance |
Michael Fuhr <mike(at)fuhr(dot)org> writes:
> Further tests show that for this application
> the killer is stats_command_string, not stats_block_level or
> stats_row_level.
I tried it with pgbench -c 10, and got these results:
41% reduction in TPS rate for stats_command_string
9% reduction in TPS rate for stats_block/row_level (any combination)
strace'ing a backend confirms my belief that stats_block/row_level send
just one stats message per transaction (at least for the relatively
small number of tables touched per transaction by pgbench). However
stats_command_string sends 14(!) --- there are seven commands per
pgbench transaction and each results in sending a <command> message and
later an <IDLE> message.
Given the rather lackadaisical way in which the stats collector makes
the data available, it seems like the backends are being much too
enthusiastic about posting their stats_command_string status
immediately. Might be worth thinking about how to cut back the
overhead by suppressing some of these messages.
regards, tom lane
From | Date | Subject | |
---|---|---|---|
Next Message | Jim C. Nasby | 2005-12-13 03:39:46 | Re: [GENERAL] missing something obvious about intervals? |
Previous Message | Andrew Dunstan | 2005-12-13 03:12:41 | Re: 7.3 failure on platypus |
From | Date | Subject | |
---|---|---|---|
Next Message | Simon Riggs | 2005-12-13 22:31:29 | Re: Inherited Constraints |
Previous Message | Michael Fuhr | 2005-12-13 01:07:51 | Re: How much expensive are row level statistics? |
From | Date | Subject | |
---|---|---|---|
Next Message | Tom Lane | 2005-12-13 04:17:51 | Re: Memory Leakage Problem |
Previous Message | Michael Fuhr | 2005-12-13 01:07:51 | Re: How much expensive are row level statistics? |