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 20:07:46 +0530
Message-ID: <a301bfd90908030737p6c1eba91u8bb413647ce18679@mail.gmail.com> (raw)
In-Reply-To: <9837222c0908030730kd59b9c2v7583666c5716aead@mail.gmail.com>
References: <200907311459.n6VExuSa036743@wwwmaster.postgresql.org>
<20090731234901.GD11098@alvh.no-ip.org>
<9837222c0908010828x7182494av3fd5909b64f4b2ad@mail.gmail.com>
<a301bfd90908030647l350f6348ne1231bb9fd113280@mail.gmail.com>
<9837222c0908030656m6ed69a26gc90a6c94b41a4c47@mail.gmail.com>
<a301bfd90908030712h3668b135g16cce3a12c332a93@mail.gmail.com>
<9837222c0908030716r416d789ewef3f77c65b39d916@mail.gmail.com>
<a301bfd90908030720m564e2372j4ef5257be15cabaf@mail.gmail.com>
<9837222c0908030730kd59b9c2v7583666c5716aead@mail.gmail.com>
Hi,
>>>>>
>>>>> Maybe. I'm unsure if it's enough to just try another
>>>>> WaitForSingleObjectEx() on it, or if we need to actually issue a
>>>>> WSARecv() on it as well. Maybe it would be enough to just change the
>>>>> INIFINTE on line 318 of socket.c to a fixed value. That will loop down
>>>>> to WSARecv() which should exit with WSAEWOULDBLOCK which will cause us
>>>>> to do a short sleep and come back. But we'd have to change the limit
>>>>> of 5 somehow then, since in theory we should wait forever. Maybe that
>>>>> outer loop should just be a for(;;), what do you think?
>>>>>
>>>>
>>>> Yes, line 318 seems to be a much better location to me. If Windows and
>>>> it's socket logic behaves properly most of the times :), most of the
>>>> calls should come out within the first few tries, so changing 5 to an
>>>> infinite loop shouldn't hurt those normal use cases in theory.
>>>>
>>>> OTOH, I was wondering what if we kill the stats collector and on a
>>>> restart the socket communication resumes properly. Would that
>>>> conclusively mean that it is a flaw in our code?
>>>
>>> No, if we kill the stats collector that will destroy all sockets, and
>>> when the new one starts all the sockets it operates on are fresh and
>>> new. So it doesn't show that the flaw is in our code - but it also
>>> doesn't show that it's in the kernel or runtime libraries.
>>>
>>
>> AFAICS in the code, the inherited pgStatSock socket FD remains the
>> same across the restart of the stats collector process...
>
> Partially correct, I think.
>
> Each backend has it's own handle on win32, since we use EXEC_BACKEND
> (this includes the "utility processes" like the stats collector). When
> we start the new one, we are going to use DuplicateHandle() in
> save_backend_variables(). This will therefor get it a new handle, but
> they are both pointing to the same kernel object. I don't know if
> WaitForMultipleObjectsEx() is going to see these as two different
> objects or not, but I think it does.
>
Hmm, got it. Nothing like adding more confusion into the mix :)
Regards,
Nikhils
--
http://www.enterprisedb.com
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
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: <a301bfd90908030737p6c1eba91u8bb413647ce18679@mail.gmail.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox