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Re: fork/exec patch: pre-CreateProcess finalization

From: Claudio Natoli <claudio(dot)natoli(at)memetrics(dot)com>
To: 'Tom Lane ' <tgl(at)sss(dot)pgh(dot)pa(dot)us>,Claudio Natoli <claudio(dot)natoli(at)memetrics(dot)com>
Cc: 'Bruce Momjian ' <pgman(at)candle(dot)pha(dot)pa(dot)us>,'Jan Wieck ' <JanWieck(at)Yahoo(dot)com>,"'pgsql-patches(at)postgreSQL(dot)org '" <pgsql-patches(at)postgreSQL(dot)org>
Subject: Re: fork/exec patch: pre-CreateProcess finalization
Date: 2004-01-09 06:26:39
Message-ID: A02DEC4D1073D611BAE8525405FCCE2B55F241@harris.memetrics.local (view raw or flat)
Thread:
Lists: pgsql-patches
Tom Lane wrote:

> What it comes down to is I don't want the postmaster to be keeping its
> own state in shared memory --- that is, the array must be write-only
> memory as far as the postmaster is concerned.  If we eliminate the

Ok. Well, I can appreciate things from that point of view.


> postmaster's private DLList of backends, then the postmaster becomes
> that much more vulnerable to corruption from a backend bug that leads to
> trashing shared memory.  To take just one example: backend A goes nuts,
> zeroes the whole shmem segment, and then dumps core.  How is the
> postmaster going to kill the other backends so that it can begin the
> recovery process?  If there's no record of their PIDs left anywhere,
> it's got a problem.  The postmaster *needs* its own copy of that DLList.
> 
> You might object that backend bugs could clobber the array and thus
> interfere with cancel request processing, but that's not nearly as
> critical a function.

Actually, if I was going to argue anything, I'd say that if a backend goes
nuts and zeroes the whole shmem segment you've probably some bigger things
to worry about (Aside: Would postgres actually recover from such an
occurence? BTW, I'd be pretty impressed if it did, but not all that
surprised ;-).

But I'll happily concede the point, and prove it by knocking up a patch for
it over the weekend (unless anyone else particularly wants to).

Cheers,
Claudio

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Next:From: Tom LaneDate: 2004-01-09 06:36:43
Subject: Re: fork/exec patch: pre-CreateProcess finalization
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Subject: Re: fork/exec patch: pre-CreateProcess finalization

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