Re: dynamic shared memory: wherein I am punished for good intentions

On Thu, Oct 10, 2013 at 1:13 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> (1) Define the issue as "not our problem". IOW, as of now, if you
> want to use PostgreSQL, you've got to either make POSIX shared memory
> work on your machine, or change the GUC that selects the type of
> dynamic shared memory used.
>
> (2) Default to using System V shared memory. If people want POSIX
> shared memory, let them change the default.
>
> (3) Add a new setting that auto-probes for a type of shared memory
> that works. Try POSIX first, then System V. Maybe even fall back to
> mmap'd files if neither of those works.
>
> (4) Remove the option to use POSIX shared memory. System V FTW!
>
> After some consideration, I think my vote is for option #2. Option #1
> seems too user-hostile, especially for a facility that has no in-core
> users yet, though I can imagine we might want to go that way
> eventually, especially if we at some point try to dump System V shared
> memory altogether, as has been proposed. Option #4 seems sad; we know
> that System V shared memory limits are a problem for plenty of people,
> so it'd be a shame not to have a way to use the POSIX facilities if
> they're available. Option #3 is fine as far as it goes, but it adds a
> significant amount of complexity I'd rather not deal with.
>
> Other votes? Other ideas?

I believe option 2 is not only good for now, but also a necessary
previous step in the way to option 3, which I believe should be the
goal.

So, ship a version with option 2, then implement 3, and make it the
default when enough people (using option 2) have successfully tested
pg's implementation of POSIX shared memory.