pgsql: Add: > > * Create a bitmap of pages that need vacuuming > >

Log Message:
-----------
Add:

* Create a bitmap of pages that need vacuuming

Instead of sequentially scanning the entire table, have the background
writer or some other process record pages that have expired rows, then
VACUUM can look at just those pages rather than the entire table. In
the event of a system crash, the bitmap would probably be invalidated.

Modified Files:
--------------
pgsql/doc:
TODO (r1.1563 -> r1.1564)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/TODO.diff?r1=1.1563&r2=1.1564)
pgsql/doc/src/FAQ:
TODO.html (r1.70 -> r1.71)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/TODO.html.diff?r1=1.70&r2=1.71)