/*
     * We don't need to lock the page, as we're only looking at a single
bit.
     */
    result = (map[mapByte] & (1 << mapBit)) ? true : false;


Isn't this a dangerous assumption to make ? I am not so sure that even a bit
can be read atomically on all platforms. I think the only caller of
visibilitymap_test() is VACUUM which can live with a false information. But
if this is indeed a problem, should we either fix this or have explicit
comments there ?

BTW, my apologies for random comments. I haven't followed the discussion
well, neither done a full review. So these things might have been discussed
before.

Thanks,
Pavan

-- 
Pavan Deolasee
EnterpriseDB     http://www.enterprisedb.com

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