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Re: psql query gets stuck indefinitely

From: tamanna madaan <tamanna(dot)madaan(at)globallogic(dot)com>
To: Craig Ringer <ringerc(at)ringerc(dot)id(dot)au>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: psql query gets stuck indefinitely
Date: 2011-11-29 11:26:48
Message-ID: CAD4qJ_JpJxtB4WDF5XNLtojM565obsFRnZEnKbhm1xrNwyu3LQ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-general
well, one question : Is tcp-keep-alive enabled by default in postgres-8.1.2 .

I am using postgres on linux platform .



On Tue, Nov 29, 2011 at 8:51 AM, tamanna madaan <
tamanna(dot)madaan(at)globallogic(dot)com> wrote:

> Hi Craig
>
> Thanks for your reply . But unfortunately I dont have that process running
> right now. I have already killed that process . But I have seen this
> problem sometimes on my setup.
> It generally happens when the remote system is going slow for some reason
> (CPU utilization high etc.)  . But whatever is the reason , I would assume
> that the query should return with some error or so
> in case the system, the query is running on , is rebooted .  But  it
> doesn't return and remain stuck. Moreover, the same query sometimes hangs
> even if it is run on local postgres  database so I dont think
> network issues have any role in that . Please help.
>
> Thanks....
>
> Regards
> Tamanna
>
>
> On Tue, Nov 29, 2011 at 7:58 AM, Craig Ringer <ringerc(at)ringerc(dot)id(dot)au>wrote:
>
>> On 11/28/2011 05:30 PM, tamanna madaan wrote:
>>
>>> Hi All
>>> I have postgres installed in cluster setup. My system has a script
>>> which executes the below query on remote system in cluster.
>>> psql -t -q -Uslon -h<hostip> -d<dbname> -c"select 1;"
>>> But somehow this query got stuck. It didnt return even after the remote
>>> system( on which this query was supposed to execute) is rebooted . What
>>> could be the reason ??
>>>
>>
>> I relised just after sending my last message:
>>
>> You should use ps to find out what exactly psql is doing and which system
>> call it's blocked in in the kernel (if it's waiting on a syscall). As you
>> didn't mention your OS I'll assume you're on Linux, where you'd use:
>>
>>  ps -C psql -o wchan:80=
>>
>> or
>>
>>  ps -p 1234 -o wchan:80=
>>
>> ... where "1234" is the pid of the stuck psql process. In a psql waiting
>> for command line input I see it blocked in the kernel routine "n_tty_read"
>> for example.
>>
>>
>> If you really want to know what it's doing you can also attach gdb and
>> get a backtrace to see what code it's paused in inside psql:
>>
>> gdb -q -p 1234 <<__END__
>> bt
>> q
>> __END__
>>
>> If you get a message about "missing debuginfos", lots of lines reading
>> "no debugging symbols found" or lots of lines ending in "?? ()" then you
>> need to install debug symbols. How to do that depends on your OS/distro so
>> I won't go into that; it's documented on the PostgreSQL wiki under "how to
>> get a stack trace" but you probably won't want to bother if this is just
>> for curiosity's sake.
>>
>> You're looking for output that looks like:
>>
>> #1  0x000000369d22a131 in rl_getc () from /lib64/libreadline.so.6
>> #2  0x000000369d22a8e9 in rl_read_key () from /lib64/libreadline.so.6
>> #3  0x000000369d215b11 in readline_internal_char () from
>> /lib64/libreadline.so.6
>> #4  0x000000369d216065 in readline () from /lib64/libreadline.so.6
>>
>> ... etc ...
>>
>>
>> --
>> Craig Ringer
>>
>
>
>
> --
> Tamanna Madaan | Associate Consultant | GlobalLogic Inc.
> Leaders in Software R&D Services
> ARGENTINA | CHILE | CHINA | GERMANY | INDIA | ISRAEL | UKRAINE | UK | USA
>
> Office: +0-120-406-2000 x 2971
>
> www.globallogic.com
>
>
>


-- 
Tamanna Madaan | Associate Consultant | GlobalLogic Inc.
Leaders in Software R&D Services
ARGENTINA | CHILE | CHINA | GERMANY | INDIA | ISRAEL | UKRAINE | UK | USA

Office: +0-120-406-2000 x 2971

www.globallogic.com

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