Re: Posix Shared Mem patch

On Thu, Jun 28, 2012 at 7:15 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Thu, Jun 28, 2012 at 12:13 PM, Thom Brown <thom@linux.com> wrote:
>> On 64-bit Linux, if I allocate more shared buffers than the system is
>> capable of reserving, it doesn't start.  This is expected, but there's
>> no error logged anywhere (actually, nothing logged at all), and the
>> postmaster.pid file is left behind after this failure.
>
> Fixed.
>
> However, I discovered something unpleasant.  With the new code, on
> MacOS X, if you set shared_buffers to say 3200GB, the server happily
> starts up.  Or at least the shared memory allocation goes through just
> fine.  The postmaster then sits there apparently forever without
> emitting any log messages, which I eventually discovered was because
> it's busy initializing a billion or so spinlocks.
>
> I'm pretty sure that this machine does not have >3TB of virtual
> memory, even counting swap.  So that means that MacOS X has absolutely
> no common sense whatsoever as far as anonymous shared memory
> allocations go.  Not sure exactly what to do about that.  Linux is
> more sensible, at least on the system I tested, and fails cleanly.

What happens if you mlock() it into memory - does that fail quickly?
Is that not something we might want to do *anyway*?

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 Magnus Hagander
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