I believe that all we need is the ID to be constant and unique while the postmaster or its associated backends are running. If anything from a given generation has the database open, it will remain constant before any new process can connect to it successfully. Would it be feasible to lookup the ID of an important file in the DataDir?

As far as the POSIX version goes, here is an updated patch. I changed it to use the inode/device ID instead of the filename to avoid the renaming cases. It also no longer needs the more clunky than necessary hash stuff.

Attachment: configure.in.patch
Description: Binary data

Attachment: netbsd.patch
Description: Binary data

Attachment: openbsd.patch
Description: Binary data

Attachment: posix_shmem.c
Description: Binary data

(The NetBSD/OpenBSD patches are to force those to build with the SysV shmem calls, since they are notably without POSIX shmem support.)

Chris Marcellino

On Feb 27, 2007, at 1:40 AM, Magnus Hagander wrote:

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.


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