On Sat, Aug 17, 2019 at 9:59 AM Andres Freund <and...@anarazel.de> wrote: > > Hi, > > On 2019-08-16 20:39:21 -0400, Greg Stark wrote: > > But isn't this all just silliiness these days? We could actually sum up the > > space recorded in the fsm and get a much more trustworthy number in > > milliseconds. > > You mean like pgstattuple_approx()? > > https://www.postgresql.org/docs/current/pgstattuple.html > > Or something different? > > > I rigged up a quick proof of concept and the code seems super simple and > > quick. There's one or two tables where the number is a bit suspect and > > there's no fsm if vacuum hasn't run but that seems pretty small potatoes > > for such a huge help in reducing user pain. > > Hard to comment on what you propose, without more details. But note that > you can't just look at the FSM, because in a lot of workloads it is > often hugely out of date. And fairly obviously it doesn't provide you > with information about how much space is currently occupied by dead > tuples. What pgstattuple_approx does is to use the FSM for blocks that > are all-visible, and look at the page otherwise. >
It's just an idea but we could have pgstattuple_approx use sample scan to estimate the table bloat more faster. Regards, -- Masahiko Sawada NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center
