Re: [HACKERS] What's left?

[Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>]

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.

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