Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes:
> ... I'm not sure if it would
> be safe to set the PD_ALL_VISIBLE_FLAG while holding just a shared lock,
> though. If it is, then we could do just that.
Seems like it must be safe. If you have shared lock on a page then no
one else could be modifying the page in a way that would falsify
PD_ALL_VISIBLE. You might have several processes concurrently try to
set the bit but that is safe (same situation as for hint bits).
The harder part is propagating the bit to the visibility map, but I
gather you intend to only allow VACUUM to do that?
regards, tom lane
