Re: document the need to analyze partitioned tables

On Tue, Jan 17, 2023 at 03:00:50PM -0600, Justin Pryzby wrote:
> On Tue, Jan 17, 2023 at 03:53:24PM -0500, Bruce Momjian wrote:
> > On Thu, Jan 12, 2023 at 03:27:47PM -0800, Nathan Bossart wrote:
> > > Here is my take on the wording:
> > >
> > > Since all the data for a partitioned table is stored in its partitions,
> > > autovacuum does not process partitioned tables. Instead, autovacuum
> > > processes the individual partitions that are regular tables. This
> > > means that autovacuum only gathers statistics for the regular tables
> > > that serve as partitions and not for the partitioned tables. Since
> > > queries may rely on a partitioned table's statistics, you should
> > > collect statistics via the ANALYZE command when it is first populated,
> > > and again whenever the distribution of data in its partitions changes
> > > significantly.
> >
> > Uh, what about autovacuum's handling of partitioned tables? This makes
> > it sound like it ignores them because it talks about manual ANALYZE.
>
> If we're referring to the *partitioned* table, then it does ignore them.
> See:
>
> |commit 6f8127b7390119c21479f5ce495b7d2168930e82
> |Author: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
> |Date: Mon Aug 16 17:27:52 2021 -0400
> |
> | Revert analyze support for partitioned tables

Yes, I see that patch was trying to combine the statistics of individual
partitions into a partitioned table summary.

> Maybe (all?) the clarification the docs need is to say:
> "Partitioned tables are not *themselves* processed by autovacuum."

Yes, I think the lack of autovacuum needs to be specifically mentioned
since most people assume autovacuum handles _all_ statistics updating.

Can someone summarize how bad it is we have no statistics on partitioned
tables? It sounds bad to me.

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

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