Amit, * Amit Kapila (amit.kapil...@gmail.com) wrote: > On Sun, Jan 22, 2017 at 3:27 AM, Stephen Frost <sfr...@snowman.net> wrote: > > * Simon Riggs (si...@2ndquadrant.com) wrote: > >> On 12 August 2016 at 01:01, Tom Lane <t...@sss.pgh.pa.us> wrote: > >> > Michael Paquier <michael.paqu...@gmail.com> writes: > >> >> In short, autovacuum will need to scan by itself the VM of each > >> >> relation and decide based on that. > >> > > >> > That seems like a worthwhile approach to pursue. The VM is supposed to > >> > be > >> > small, and if you're worried it isn't, you could sample a few pages of > >> > it. > >> > I do not think any of the ideas proposed so far for tracking the > >> > visibility percentage on-the-fly are very tenable. > >> > >> Sounds good, but we can't scan the VM for every table, every minute. > >> We need to record something that will tell us how many VM bits have > >> been cleared, which will then allow autovac to do a simple SELECT to > >> decide what needs vacuuming. > >> > >> Vik's proposal to keep track of the rows inserted seems like the best > >> approach to this issue. > > > > I tend to agree with Simon on this. I'm also worried that an approach > > which was based off of a metric like "% of table not all-visible" might > > result in VACUUM running over and over on a table because it isn't able > > to actually make any progress towards improving that percentage. We'd > > have to have some kind of "cool-off" period or something. > > > > Tracking INSERTs and then kicking off a VACUUM based on them seems to > > address that in a natural way and also seems like something that users > > would generally understand as it's very similar to what we do for > > UPDATEs and DELETEs. > > > > Tracking the INSERTs as a reason to VACUUM is also very natural when you > > consider the need to update BRIN indexes. > > Another possible advantage of tracking INSERTs is for hash indexes > where after split we need to remove tuples from buckets that underwent > split recently.
That's a good point also, and for clearing GIN pending lists too, now that I think about it. We really need to get this fixed for PG10. Thanks! Stephen
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