On 13-04-23 10:04 AM, Anne Rosset wrote:
Thanks Steve.
I found this: http://www.postgresql.org/docs/current/static/release-9-2-3.html
"
Fix performance problems with autovacuum truncation in busy workloads (Jan
Wieck)
Truncation of empty pages at the end of a table requires exclusive lock, but
autovacuum was coded to fail (and release the table lock) when there are conflicting
lock requests. Under load, it is easily possible that truncation would never occur,
resulting in table bloat. Fix by performing a partial truncation, releasing the
lock, then attempting to re-acquire the lock and continue. This fix also greatly
reduces the average time before autovacuum releases the lock after a conflicting
request arrives."
So that is not the fix?
No, that is the change that caused this problem. That fix addresses a
slightly different set of symptoms where the truncate as part of an
auto-vacuum doesn't happen because the lock gets pre-empted. An
unintended/undesirable consequence of that fix was that it means if
vacuum can't do the truncate stage because it can't obtain the lock in
the first place then statistics don't get updated.
(Sorry to ask a second time but I really need to make sure).
Thanks,
Anne
-----Original Message-----
From: Steve Singer [mailto:st...@ssinger.info]
Sent: Tuesday, April 23, 2013 6:33 AM
To: Anne Rosset
Cc: pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Performance with the new security release?
On 13-04-22 11:46 PM, Anne Rosset wrote:
Thanks Steve.
I have read that a fix has been put in release 9.2.3 for this issue. Is that
right?
Thanks,
Anne
No this issue is present in 9.0.13, 9.1.9 and 9.2.4 (as well as 9.2.3).
There is talk about fixing this for the next set of minor releases but I
haven't yet seen a patch.
-----Original Message-----
From: Steve Singer [mailto:st...@ssinger.info]
Sent: Monday, April 22, 2013 4:35 PM
To: Anne Rosset
Cc: pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Performance with the new security release?
On 13-04-22 04:41 PM, Anne Rosset wrote:
Hi Steve,
Yes I see these messages in our log. Is there a solution to this?
Thanks,
Anne
A manual analyze of the effected tables should work and give you updated
statistics. If your problem is just statistics then that should help.
A manual vacuum will , unfortunately, behave like the auto-vacuum. The only way
to get vacuum past this (until this issue is fixed) is for
vacuum to be able to get that exclusive lock. If there are times of
the day your database is less busy you might have some luck turning off
auto-vacuum on these tables and doing manual vacuums during those times.
-----Original Message-----
From: Steve Singer [mailto:st...@ssinger.info]
Sent: Monday, April 22, 2013 1:26 PM
To: Anne Rosset
Cc: pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Performance with the new security release?
On 13-04-22 04:15 PM, Anne Rosset wrote:
Hi Steve,
Thanks for your reply.
We are now running 9.0.13. Before it was 9.0.7.
How can I find out if we are running into this issue: "ie if
statistics are no longer being updated because analyze can't get the exclusive lock
for truncation"?
This issue is discussed in the thread
http://www.postgresql.org/message-id/CAMkU=1xYXOJp=jLAASPdSAqab-HwhA_
t
nRhy+JUe=4=b=v3...@mail.gmail.com
If your seeing messages in your logs of the form:
automatic vacuum of table XXX.YYY cannot (re)acquire exclusive lock for truncate
scan"
then you might be hitting this issue.
I will dig into our logs to see for the query times.
Thanks,
Anne
-----Original Message-----
From: Steve Singer [mailto:st...@ssinger.info]
Sent: Monday, April 22, 2013 12:59 PM
To: Anne Rosset
Cc: pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Performance with the new security release?
On 13-04-22 01:38 PM, Anne Rosset wrote:
Hi,
We are seeing some overall performance degradation in our application
since we installed the security release. Other commits were
also done at the same time in the application so we don't know yet if the
degradation has any relationship with the security release.
While we are digging into this, I would like to know if it is possible
that the release has some impact on performance. After reading this
"It was created as a side effect of a refactoring effort to make
establishing new connections to a PostgreSQL server faster, and the
associated code more maintainable.", I am thinking it is quite possible.
Please let me know. Thanks,
Exactly which version of PostgreSQL are you running? (we released security
update releases for multiple PG versions). Also which version were you running
before?
There were some changes to analyze/vacuum in the previous set of minor releases
that could cause performance issues in some cases (ie if statistics are no
longer being updated because analyze can't get the
exclusive lock for truncation). There might be other unintended
performance related changes.
Are all queries taking longer or only some? Can you find any sort of pattern
that might help narrow the issue?
Steve
Anne
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