On Thu, Jul 14, 2022 at 4:31 PM Andres Freund <andres@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..."
