From: Nikhil Sontakke <nikhil.sontakke@enterprisedb.com>
To: Magnus Hagander <magnus@hagander.net>
Cc: Alvaro Herrera <alvherre@commandprompt.com>
Cc: Luke Koops <luke.koops@entrust.com>
Cc: pgsql-bugs@postgresql.org
Subject: Re: BUG #4958: Stats collector hung on WaitForMultipleObjectsEx while attempting to recv a datagram
Date: Mon, 3 Aug 2009 19:17:17 +0530
Message-ID: <a301bfd90908030647l350f6348ne1231bb9fd113280@mail.gmail.com> (raw)
In-Reply-To: <9837222c0908010828x7182494av3fd5909b64f4b2ad@mail.gmail.com>
References: <200907311459.n6VExuSa036743@wwwmaster.postgresql.org>
<20090731234901.GD11098@alvh.no-ip.org>
<9837222c0908010828x7182494av3fd5909b64f4b2ad@mail.gmail.com>
Hi,
>>
>>
>>> ntdll.dll!NtWaitForMultipleObjects+0xc
>>> kernel32.dll!WaitForMultipleObjectsEx+0x11a
>>> postgres.exe!pgwin32_waitforsinglesocket+0x1ed
>>> postgres.exe!pgwin32_recv+0x90
>>> postgres.exe!PgstatCollectorMain+0x17f
>>> postgres.exe!SubPostmasterMain+0x33a
>>> postgres.exe!main+0x168
>>> postgres.exe!__tmainCRTStartup+0x10f
>>> kernel32.dll!BaseProcessStart+0x23
>>
>> I have seen this problem too. The process seems stuck for no good
>> reason. I wondered at the time if it could be a kernel issue. I
>> remember trying to send some data to the collector to verify whether
>> it'd wake up, but no luck. (I mean I couldn't find a way to do it on
>> Windows).
>
> I have seen this as well, but only in cases where there has been
> broken firewall software or such things involved. I have seen a couple
> of reports from the field though.
>
> Anyway, this really is a should-never-happen thing. As soon as a new
> packet is sent in, WaitForMultipleObjectsEx() should return right
> away. And given that backends regularly send packets over, it
> shouldn't be an issue even if we miss one...
>
And this fact should lend credence to Alvaro's (as well as mine)
suspicions that it seems to be a Windows kernel issue.
As a consequence, Magnus I was wondering if having a loop similar to
the WRITE handling of waiting for a fixed timeout in a loop (rather
than an INFINITE call to WaitForMultipleObjectsEx) inside the
pgwin32_waitforsinglesocket() function will help for the READ case
too? I believe Teogor Sigaev had raised a similar concern a while back
about it:
http://www.nabble.com/-GENERAL--Stats-collector-frozen--td8569977i20.html
Regards,
Nikhils
--
http://www.enterprisedb.com
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To: pgsql-bugs@postgresql.org
Cc: nikhil.sontakke@enterprisedb.com, magnus@hagander.net, alvherre@commandprompt.com, luke.koops@entrust.com
Subject: Re: BUG #4958: Stats collector hung on WaitForMultipleObjectsEx while attempting to recv a datagram
In-Reply-To: <a301bfd90908030647l350f6348ne1231bb9fd113280@mail.gmail.com>
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