Re: Pre-allocation of shared memory ...

OK, doc patch attached and applied. Improvements?

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Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > What really kills [:-)] me is that they allocate memory assuming I will
> > not be using it all, then terminate the executable in an unrecoverable
> > way when I go to use the memory.
>
> To be fair, I'm probably misstating things by referring to malloc().
> The big problem probably comes from fork() with copy-on-write --- the
> kernel has no good way to estimate how much of the shared address space
> will eventually become private modified copies, but it can be forgiven
> for wanting to make less than the worst-case assumption.
>
> Still, if you are wanting to run a reliable server, I think worst-case
> assumption is exactly what you want. Swap space is cheap, and there's
> no reason you shouldn't have enough swap to support the worst-case
> situation. If the swap area goes largely unused, that's fine.
>
> The policy they're calling "paranoid overcommit" (don't allocate more
> virtual memory than you have swap) is as far as I know the standard on
> all Unixen other than Linux; certainly it's the traditional behavior.
>
> regards, tom lane
>

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