From: | Greg Stark <gsstark(at)mit(dot)edu> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Greg Stark <gsstark(at)mit(dot)edu>, Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com>, pgsql-general <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: not exactly a bug report, but surprising behaviour |
Date: | 2003-02-05 19:05:24 |
Message-ID: | 873cn25z0r.fsf@stark.dyndns.tv |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-general |
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
> Greg Stark <gsstark(at)mit(dot)edu> writes:
> > I'm watching this query I'm working on now drive the cpu to 100% for 6+ hours
> > with virtually no I/O. And I think it's the best I can do. All the times is
> > being spent moving bits around from one place to another.
>
> It would be interesting to see a gprof profile of that.
Ok, I have a copy of postgres built with -pg now. I'm running grpof on the
gmon.out file but all I'm seeing is this:
% cumulative self self total
time seconds seconds calls ms/call ms/call name
100.00 0.01 0.01 1 10.00 10.00 InitFreeSpaceMap
0.00 0.01 0.00 12296 0.00 0.00 LWLockAssign
0.00 0.01 0.00 323 0.00 0.00 GUC_yylex
0.00 0.01 0.00 123 0.00 0.00 ShmemAlloc
0.00 0.01 0.00 123 0.00 0.00 tas
0.00 0.01 0.00 79 0.00 0.00 AllocSetFreeIndex
...
I assume this is only the postmaster initialization as I've run a smaller
version of the job which took 8 minutes. Is there an easy trick to getting
gmon.out output from a specific backend process?
> > It occurs to me that it's possible postgres is doing this already at a lower
> > level of abstraction.
>
> Yes, tuplesort.c has heard of pushing pointers around rather than
> copying records. I wonder though whether data is being pushed out to
> kernel disk buffers and then back in again --- do you have sort_mem
> set large enough?
Yes, this is the job I asked about sort_mem for. I have it up to 64M and no
pgsql_tmp files are being created.
> Another likely theory is that the interface layers needed to access
> datatype-specific comparison routines are chewing the cycles. Need facts not
> speculation to know where the bottleneck is...
--
greg
From | Date | Subject | |
---|---|---|---|
Next Message | Tom Lane | 2003-02-05 19:16:37 | Re: Is 7.3.2 out? |
Previous Message | Oleg Bartunov | 2003-02-05 19:04:32 | Alpha version of contrib/tsearch is available for testing |