Re: Estimating total amount of shared memory required by postmaster

Excerpts from Tom Lane's message of jue jun 02 15:49:53 -0400 2011:
> Alexey Klyukin <alexk@commandprompt.com> writes:

> > - Try to actually allocate the shared memory in a way postmaster does this
> >   nowadays, if the process fails - analyze the error code to check whether the
> >   failure is due to the shmmax or shmmall limits being too low. This would
> >   need to be run as a separate process (not postmaster's child) to avoid
> >   messing with the postmaster's own shared memory, which means that this would
> >   be hard to implement as a user-callable stored function.
> 
> The results of such a test wouldn't be worth the electrons they're
> written on anyway: you're ignoring the likelihood that two instances of
> shared memory would overrun the kernel's SHMALL limit, when a single
> instance would be fine.
> 
> Given that you can't do it in the context of a live installation, just
> trying to start the postmaster and seeing if it works (same as initdb
> does) seems as good as anything else.

BTW the other idea we discussed at PGCon was that we could have a
postmaster option that would parse the config file and then report the
amount of shared memory needed to run with it.  If we had that, then
it's easy to write a platform-specific shell script or program that
verifies that the given number is within the allowed limits.

-- 
Álvaro Herrera <alvherre@commandprompt.com>
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