Re: VACUUM and ANALYZE disagreeing on what reltuples means

Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
> On 7/25/17 12:55 AM, Tom Lane wrote:
>> I think the planner basically assumes that reltuples is the live
>> tuple count, so maybe we'd better change VACUUM to get in step.

> Attached is a patch that (I think) does just that. The disagreement was
> caused by VACUUM treating recently dead tuples as live, while ANALYZE
> treats both of those as dead.

> At first I was worried that this will negatively affect plans in the
> long-running transaction, as it will get underestimates (due to
> reltuples not including rows it can see). But that's a problem we
> already have anyway, you just need to run ANALYZE in the other session.

This definitely will have some impact on plans, at least in cases where
there's a significant number of unvacuumable dead tuples. So I think
it's a bit late for v10, and I wouldn't want to back-patch at all.
Please add to the next commitfest.

regards, tom lane