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Re: POSIX shared memory support

From: Magnus Hagander <magnus(at)hagander(dot)net>
To: Chris Marcellino <cmarcellino(at)apple(dot)com>
Cc: pgsql-patches(at)postgresql(dot)org
Subject: Re: POSIX shared memory support
Date: 2007-02-27 09:40:07
Message-ID: 20070227094007.GI12721@svr2.hagander.net (view raw or flat)
Thread:
Lists: pgsql-patches
On Tue, Feb 27, 2007 at 10:30:15AM +0100, Magnus Hagander wrote:
> > Does Windows have a method to get a unique ID number for a given data  
> > directory, or a token file in that directory? It would need to be  
> > constant while the database is open. Perhaps  
> > GetFileInformationByHandle? It returns a struct with a nFileIndex  
> > value that seems to be that, although I'm not certain.
> > This might make it easier to avoid the complexity of fitting the  
> > filename in the segment name, and avoid the rename problem,
> 
> Yes, you could use the fileindex value. You need that one and the volume
> serial number, total of 64+32 bits of data.
> 
> So yeah, we cuold use that instead of the full path name if we want to.
> The advantage of this one is that it's shorter, the advantage of the
> full path name is that you can see where the backend is from.
> 
> However, in most cases you will be able to see where the backend is from
> anyway, because it is likely to have some other file open in the data
> directory, so maybe that isn't such a big point after all?

Actually, I'm not sure we can. It's only stable as long as someone has
the file open. It will change if it's closed and re-opened later.

Given that we don't actually open the directory, and only files inside
it, I don't know how that works.

//Magnus

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