On Tue, Sep 6, 2016 at 2:51 PM, Simon Riggs <si...@2ndquadrant.com> wrote: > On 6 September 2016 at 19:23, Robert Haas <robertmh...@gmail.com> wrote: >> On Tue, Sep 6, 2016 at 2:16 PM, Simon Riggs <si...@2ndquadrant.com> wrote: >>> What occurs to me is that we can exactly predict how many tuples we >>> are going to get when we autovacuum, since we measure that and we know >>> what the number is when we trigger it. >>> >>> So there doesn't need to be any guessing going on at all, nor do we >>> need it to be flexible. >> >> No, that's not really true. A lot can change between the time it's >> triggered and the time it happens, or even while it's happening. >> Somebody can run a gigantic bulk delete just after we start the >> VACUUM. > > Which wouldn't be removed by the VACUUM, so can be ignored.
OK, true. But I still think it's very unlikely that we can calculate an exact count of how many dead tuples we might run into. I think we shouldn't rely on the stats collector to be perfectly correct anyway - for one thing, you can turn it off - and instead cope with the uncertainty. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers