visibility maps

/*
* 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