From: Tom Lane <tgl@sss.pgh.pa.us>
To: Josh Kupershmidt <schmiddy@gmail.com>
Cc: Chris <lists@deksai.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: stats collector suddenly causing lots of IO
Date: Fri, 16 Apr 2010 12:25:46 -0400
Message-ID: <10744.1271435146@sss.pgh.pa.us> (raw)
In-Reply-To: <i2y4ec1cf761004160854z3d040cffjc83da673f3dbf6dd@mail.gmail.com>
References: <20100413170105.GA29571@chris-laptop.a2hosting.com>
<25952.1271370711@sss.pgh.pa.us>
<20100416151900.GA3179@chris-laptop.a2hosting.com>
<9857.1271431787@sss.pgh.pa.us>
<i2y4ec1cf761004160854z3d040cffjc83da673f3dbf6dd@mail.gmail.com>
Josh Kupershmidt <schmiddy@gmail.com> writes:
> I made a small half-empty table like this:
> CREATE TABLE test_vacuum (i int PRIMARY KEY);
> INSERT INTO test_vacuum (i) SELECT a FROM generate_series(1,500000) AS a;
> DELETE FROM test_vacuum WHERE RANDOM() < 0.5;
> and then ran:
> VACUUM test_vacuum;
> while an strace of the stats collector process was running. Then after
> a few seconds, found the PID of the VACUUM process, and ran strace on
> it. I killed them after the VACUUM finished. Outputs attached.
Huh. The VACUUM strace clearly shows a boatload of TABPURGE messages
being sent:
sendto(7, "\2\0\0\0\350\3\0\0\5@\0\0\366\0\0\0\324\206<\24\321uC\24\320\350)\24\225\345,\24"..., 1000, 0, NULL, 0) = 1000
sendto(7, "\2\0\0\0\350\3\0\0\5@\0\0\366\0\0\0C\274?\24\365\323?\24\241N@\24\217\0309\24"..., 1000, 0, NULL, 0) = 1000
sendto(7, "\2\0\0\0\350\3\0\0\5@\0\0\366\0\0\0\375Z2\24\211\f@\0241\3047\24\357mH\24"..., 1000, 0, NULL, 0) = 1000
sendto(7, "\2\0\0\0\350\3\0\0\5@\0\0\366\0\0\0\242\3529\24\234K\'\24\17\227)\24\300\22+\24"..., 1000, 0, NULL, 0) = 1000
and the stats collector is receiving them:
recvfrom(7, "\2\0\0\0\350\3\0\0\5@\0\0\366\0\0\0\324\206<\24\321uC\24\320\350)\24\225\345,\24"..., 1000, 0, NULL, NULL) = 1000
recvfrom(7, "\2\0\0\0\350\3\0\0\5@\0\0\366\0\0\0C\274?\24\365\323?\24\241N@\24\217\0309\24"..., 1000, 0, NULL, NULL) = 1000
recvfrom(7, "\2\0\0\0\350\3\0\0\5@\0\0\366\0\0\0\375Z2\24\211\f@\0241\3047\24\357mH\24"..., 1000, 0, NULL, NULL) = 1000
So this *should* have resulted in the stats file shrinking. Did you
happen to notice if it did, after you did this?
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, schmiddy@gmail.com, lists@deksai.com
Subject: Re: stats collector suddenly causing lots of IO
In-Reply-To: <10744.1271435146@sss.pgh.pa.us>
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