(back from vacation)
Tom Lane wrote:
I wrote:
Another interesting question is why successive vacuums aren't causing
the index reltuples counts to go to zero. Shouldn't a partial vacuum
result in *all* pages of the relation being marked as not needing to
be examined by the next vacuum?
I figured out the reason for that: the first 32 pages of the table are
always scanned, even if the whole thing is frozen, because of the
SKIP_PAGES_THRESHOLD logic. We could change that behavior by
initializing all_visible_streak to SKIP_PAGES_THRESHOLD instead of zero.
But if we did so then having even just page zero be skippable would mean
that we clear scanned_all and thus fail to update reltuples, which is
probably not a good thing.
Right, that's exactly why I wrote it like that. I also thought about
scanning the (beginning of the) visibility map first to see if there's
big enough gaps in there to warrant skipping pages, but went with the
current approach because it's so much simpler.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
