On 2013-05-23 19:51:48 +0200, Andres Freund wrote: > We currently need to make sure we scanned the whole relation and have > frozen everything to have a sensible relfrozenxid for a relation. > > So, what I propose instead is basically: > 1) only vacuum non-all-visible pages, even when doing it for > anti-wraparound > 2) When we can set all-visible guarantee that all tuples on the page are > fully hinted. During recovery do the same, so we don't need to log > all hint bits. > We can do this with only an exclusive lock on the buffer, we don't > need a cleanup lock. > 3) When we cannot mark a page all-visible or we cannot get the cleanup > lock, remember the oldest xmin on that page. We could set all visible > in the former case, but we want the page to be cleaned up sometime > soonish. > 4) If we can get the cleanup lock, purge dead tuples from the page and > the indexes, just as today. Set the page as all-visible. > > That way we know that any page that is all-visible doesn't ever need to > look at xmin/xmax since we are sure to have set all relevant hint > bits.
Heikki noticed that I made quite the omission here which is that you would need to mark tuples as all visible as well. I was thinking about using HEAP_MOVED_OFF | HEAP_MOVED_IN as a hint for that. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
