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To: Horak Daniel <horak AT mmp DOT plzen-city DOT cz>
cc: "'pgsql-hackers AT postgreSQL DOT org'" <pgsql-hackers AT postgreSQL DOT org>,
        "'cygwin AT sourceware DOT cygnus DOT com'" <cygwin AT sourceware DOT cygnus DOT com>,
        "'Joost Kraaijeveld'" <JKraaijeveld AT askesis DOT nl>
Subject: Re: [HACKERS] backend freezeing on win32 fixed (I hope ;-) ) 
In-reply-to: Your message of Mon, 16 Aug 1999 11:35:54 +0200 
             <2E7F82FAC1FCD2118E1500A024B3BF907DED3B AT exchange DOT mmp DOT plzen-city DOT cz> 
Date: Mon, 16 Aug 1999 10:07:00 -0400
Message-ID: <601.934812420@sss.pgh.pa.us>
From: Tom Lane <tgl AT sss DOT pgh DOT pa DOT us>

Horak Daniel <horak AT mmp DOT plzen-city DOT cz> writes:
> I think I have fixed the freezing of the postgres backend on Windows NT. Now
> it survives 5 regression test in a cycle with some concurrent connections
> during running the tests.
> It have looked like a problem with initializing the same semaphore for
> second time (they are "preinitialized" for performance reasons in
> InitProcGlobal() in storage/lmgr/proc.c)

They should never be "initialized a second time".  And the preallocation
is *not* for performance reasons, it is to make sure we can actually get
enough semaphores (rather than dying under load when we fail to get the
N+1'st semaphore when starting the N+1'st backend).

> The fix (made for v6.5.1) is here:
> [ Fix consists of diking out preallocation of semaphores by postmaster ]

I do not like this patch one bit --- I think it is voodoo that doesn't
really have anything to do with the true problem.  I don't know what
the true problem is, mind you, but I don't think this is the way to
fix it.

Is it possible that the CygWin environment doesn't have a correct
emulation of IPC semaphores, such that a sema allocated by one process
(the postmaster) is not available to other procs (the backends)?
That would explain preallocation not working --- but if that's it then
we have major problems in other places, since the code assumes that a
sema once allocated will remain available to later backends.

			regards, tom lane

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