Visibility map and hint bits

There has been a lot of recent discussion about the visibility map (for
index-only scans) and hint bits (trying to avoid double-writing a
table).

I wonder if we could fix both of these at the same time.  Once the
visibility map is reliable, can we use that to avoid updating the hint
bits on all rows on a page?

For bulk loads, all the pages are going have the same xid and all be
visible, so instead of writing the entire table, we just write the
visibility map.

I think the problem is that we have the PD_ALL_VISIBLE page flag, which
requires a write of the page as well.  Could we get by with only the
visibility bits and remove PD_ALL_VISIBLE?

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + It's impossible for everything to be true. +