Yes, that is understandable. I'm not sure that there is a robust portable solution that doesn't involve a major rearchitecture. I'm not sure that would be worth the risk given the reward.


On Apr 2, 2008, at 8:50 AM, Bruce Momjian wrote:

The original patch author:

       Chris Marcellino <[EMAIL PROTECTED]>

was not CC'ed as part of this email thread. That was a mistake. Chris,
the email thread discussing your patch is here: msg01262.php

Please read the discussion --- the bottom line is that there isn't much
support for the patch.  Magnus was able to do the POSIX usage without
relying on shared memory, but I just talked to him via IM and he said it
used a Win32-specific feature that isn't portable to Unix.

I am holding this patch for the next commit fest in hopes you can adjust
it, but if not the patch will be rejected at that time.


Stephen Frost wrote:
-- Start of PGP signed section.
Chris, et al,

(commit-fest consensus discussion)
* Chris Marcellino wrote:
In case you haven't had enough, here is another version of the code
to make Postgres use POSIX shared memory. Along with the issues that
have already been addressed, this version ensures that orphaned
backends are not in the database when restarting Postgres by using a
single 1 byte SysV segment to see who is attached to the segment
using shmctl/IPC_STAT/nattach.

This really feels like a deal-breaker to me. My first reaction to this patch, honestly, is that it's being justified for all the wrong reasons. Changing to POSIX shm seems like a reasonable goal in general, provided
it can do what we need, but doing it to work around silly defaults
doesn't really work for me. If the real issue you have is with the SysV limits then I'd suggest you bring that up with the kernel/ distribution
folks to get them to use something more sane.

Looking around a bit, it looks like it's already being addressed in some
places, for example Solaris 10 apparently uses 1/4th of memory, while
Centos 5 uses 4GB.  Suse also uses a larger default, from what I
understand.  Supporting this effort to get it raised on various
platforms and distributions seems like a much better approach.

Additionally, it strikes me that there *is* a limit on POSIX shared
memory too, generally half of ram on the systems I've looked at, but
there's no guarentee that'll always be the default or that half of ram
will always be enough for us.  So, even with this change, the problem
isn't completely 'solved'.

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.


-- End of PGP section, PGP failed!

 Bruce Momjian  <[EMAIL PROTECTED]>

 + If your life is a hard drive, Christ can be your backup. +

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