Re: Feature: POSIX Shared memory support, round 2

That is strange, because the majority of the comments are new. Much
of the code and comments are reused from the SysV code because, you
know, this is an enhancement. The comments that are left serve a
purpose.
In PGSharedMemoryCreate, this implementation avoids the need to tell
if live backends are attached to an existing segment, since exisiting
segments are not reattached to--the old segments are cleared when the
live orphan backends die.
I would love to hear some specific, less sweeping, comments about how
the code is actually written and functions. Otherwise, I'll try to
refactor this and return once again.

Thank you,
Chris Marcellino


On Feb 9, 2007, at 6:40 AM, Tom Lane wrote:

> Chris Marcellino <cmarcellino@apple.com> writes:
>> Here is a new patch that uses the POSIX api's. It encodes the
>> canonical path (see 'man realpath') of the database's data directory
>> into the shared memory segment name using an strong hash function to
>> make it fit in the shared memory segment name under all cases,
>> without risk of key collision.
>
> I find this patch utterly unreadable, because of your cavalier
> disregard
> for making the comments match the truth.  You have copied-and-
> pasted the
> original SysV code and fixed some small fraction of the comments,
> and I
> cannot tell which ones still reflect reality --- but I can tell that a
> lot of them don't.
>
> Also, I don't see where this implements any sort of detection of live
> backends attached to an existing segment, so I don't think you have
> responded to that objection.  Magnus' idea for Windows was to use a
> segment set up to automatically go away as soon as the last attacher
> died, but AFAICT that isn't how this works.
>
>             regards, tom lane
>
> ---------------------------(end of
> broadcast)---------------------------
> TIP 7: You can help support the PostgreSQL project by donating at
>
>                 http://www.postgresql.org/about/donate