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Re: [pgsql-hackers-win32] What's left?

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>,Claudio Natoli <claudio(dot)natoli(at)memetrics(dot)com>,"''Merlin Moncure' '" <merlin(dot)moncure(at)rcsonline(dot)com>,"'pgsql-hackers-win32 '" <pgsql-hackers-win32(at)postgresql(dot)org>
Subject: Re: [pgsql-hackers-win32] What's left?
Date: 2004-01-27 01:51:12
Message-ID: 200401270151.i0R1pCo21623@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-hackers-win32pgsql-patches
Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > In this way, no one ever has the rename file open while we are holding
> > the locks, and we can loop without holding an exclusive lock on
> > pg_shadow, and file writes remain in order.
> 
> You're doing this where exactly, and are certain that you are holding no
> locks why exactly?  And if you aren't holding a lock, what prevents
> concurrency bugs?

I am looking now at the relcache file, pg_pwd and pg_group.  I am sure I
am holding some locks, but not an exclusive lock on e.g. pg_shadow. I am
working on a patch now.  I don't expect to eliminate the looping for
rename, but to eliminate holding exclusive locks while doing the rename
to a file actively being read.  By using realfile.new, the first rename
is only being done on a file that is never opened, just renamed, which
should be quick.

I can't think of a cleaner solution.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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