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Re: Strange behavior with large datas

From: "Cyril VELTER" <cyril(dot)velter(at)metadys(dot)com>
To: <pgsql-cygwin(at)postgresql(dot)org>
Subject: Re: Strange behavior with large datas
Date: 2001-08-21 18:32:53
Message-ID: 01db01c12a6f$b41201e0$6901a8c0@Serveur (view raw or flat)
Thread:
Lists: pgsql-cygwin
    Jason,

> >     I've done some test to find where libpq hang. It does hang on the
recv
> > call of fe-misc.c line 444. When it hangs, all datas have already been
read
> > successfully on the socket, so recv should return 0 on a non blocking
> > socket?
>
> recv should return -1 with errno set to EAGAIN in nonblocking mode when
> no data is available.

    OK, it does make sense. But the call to recv just block forever when all
datas are received. I suspect the problem is in cygwin (using cygwin 1.3.1-1
doens't show this problem, but there is the slow update on large fields
...).

> Did you workaround this problem by modifying the PostgreSQL code? If
> so, then please try to determine whether the problem is in Cygwin (most
> likely) or PostgreSQL.  If in Cygwin, then please report it to the Cygwin
> list (cygwin(at)cygwin(dot)com) with a small test case, if possible.

    Yes, the workaround is a small modification of fe-misc.c to test data
availability before calling recv. I can make a report to cygwin, but I'm not
enought a sockets guru to write a small test case. Perhaps the strace output
of a session which hang at the end migh help them?


> You can find the above at:
>
>
http://members.home.net/jtishler/software/postgresql/postgresql-7.1.2-1-win3
2.tar.gz


    Thanks,

        This lib also have a problem with large reads, but instead of
hanging completly, an error is returned. I have eared recently some
discussion on Hacker regarding some problems with large queries with win32
libpq. Maybe it's related ?

        I'm using win2000 sp2 if it matters.

            cyril



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