On Thu, Jul 14, 2022 at 4:31 PM Andres Freund <and...@anarazel.de> wrote:
> Hi, > > I had missed David's original email on this topic... > > On 2022-07-14 18:58:09 -0400, Bruce Momjian wrote: > > On Wed, Apr 20, 2022 at 04:40:44PM -0700, David G. Johnston wrote: > > > The new cumulative stats subsystem no longer has a "lost under heavy > load" > > > problem so that parenthetical should go (or at least be modified). > > > > > > These stats can be reset so some discussion about how the system uses > them > > > given that possibility seems like it would be good to add here. I'm > not sure > > > what that should look like though. > > > > > > diff --git a/doc/src/sgml/maintenance.sgml > b/doc/src/sgml/maintenance.sgml > > > index 04a04e0e5f..360807c8f9 100644 > > > --- a/doc/src/sgml/maintenance.sgml > > > +++ b/doc/src/sgml/maintenance.sgml > > > @@ -652,9 +652,8 @@ vacuum insert threshold = vacuum base insert > threshold + > > > vacuum insert scale fac > > > tuples to be frozen by earlier vacuums. The number of obsolete > tuples and > > > the number of inserted tuples are obtained from the cumulative > statistics > > > system; > > > it is a semi-accurate count updated by each > <command>UPDATE</command>, > > > - <command>DELETE</command> and <command>INSERT</command> > operation. (It is > > > - only semi-accurate because some information might be lost under > heavy > > > - load.) If the <structfield>relfrozenxid</structfield> value of > the table > > > + <command>DELETE</command> and <command>INSERT</command> operation. > > > + If the <structfield>relfrozenxid</structfield> value of the table > > > is more than <varname>vacuum_freeze_table_age</varname> > transactions old, > > > an aggressive vacuum is performed to freeze old tuples and advance > > > <structfield>relfrozenxid</structfield>; otherwise, only pages > that have > > > been modified > > > > Yes, I agree and plan to apply this patch soon. > > It might make sense to still say semi-accurate, but adjust the explanation > to > say that stats reporting is not instantaneous? > > Unless that delay manifests in executing an UPDATE in a session then looking at these views in the same session and not seeing that update reflected I wouldn't mention it. Concurrency aspects are reasonably expected here. But if we do want to mention it maybe: "...it is an eventually-consistent count updated by..." David J.
