Hi,
It seems to me that we could easily reclaim a bit more dead tuples in a
vacuum by recalculating the OldestXmin every now and then. In a large
table with a constant stream of updates/deletes and concurrent vacuums,
this could make a big difference.
With the attached patch, OldestXmin is recalculated in a vacuum every
100 pages. That's a quite arbitrary number, but feels like a good one to me.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com