Re: [HACKERS] Atomics for heap_parallelscan_nextpage()

On Wed, Aug 16, 2017 at 1:44 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I was feeling a bit uncomfortable with the BUFFERALIGN_DOWN() for a
> different reason: if the caller has specified the exact amount of space it
> needs, having shm_toc_create discard some could lead to an unexpected
> failure.

Well, that's why Heikki also patched shm_toc_estimate.  With the
patch, if the size being used in shm_toc_create comes from
shm_toc_estimate, it will always be aligned and nothing bad will
happen.  If the user invents another size out of whole cloth, then
they might get a few bytes less than they expect, but that's what you
get for not using shm_toc_estimate().

-- 
Robert Haas
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