From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Stephen Frost <sfrost(at)snowman(dot)net> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: POSIX shared memory support |
Date: | 2008-03-31 17:46:40 |
Message-ID: | 15231.1206985600@sss.pgh.pa.us |
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Lists: | pgsql-hackers pgsql-patches |
Stephen Frost <sfrost(at)snowman(dot)net> writes:
> Finding a way for POSIX shm to do what we need, including Tom's
> concerns, without depending on SvsV shm as a crutch work around, would
> make this change much more reasonable and could be justified as moving
> to a well defined POSIX standard, and means we may be able to support
> platforms which either are new and don't implement SysV but just POSIX,
> or cases where SysV is being actively depreceated. Neither of which is
> possible if we're stuck with using it in some cases.
Yeah, I would be far more interested in this patch if it avoided needing
SysV shmem at all. The problem is to find an adequate substitute for
the nattch-based interlock against live children of a dead postmaster.
It's possible that file locking could be used instead, but that has its
own set of portability and reliability issues to address. For example:
ISTR that on some NFS configurations, file locking silently doesn't
work, or might silently fail after it worked before, if the lock server
daemon should happen to crash. And I don't even know what's available
on Windows. So it'd need some research to make a credible proposal
along those lines.
regards, tom lane
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