Re: document the need to analyze partitioned tables

On Thu, Jan 12, 2023 at 03:27:47PM -0800, Nathan Bossart wrote:
> On Wed, Oct 05, 2022 at 10:37:01AM +0200, Laurenz Albe wrote:
> > On Mon, 2022-03-28 at 15:05 +0200, Tomas Vondra wrote:
> >> I've pushed the last version, and backpatched it to 10 (not sure I'd
> >> call it a bugfix, but I certainly agree with Justin it's worth
> >> mentioning in the docs, even on older branches).
> >
> > I'd like to suggest an improvement to this. The current wording could
> > be read to mean that dead tuples won't get cleaned up in partitioned tables.
>
> Well, dead tuples won't get cleaned up in partitioned tables, as
> partitioned tables do not have storage. But I see what you mean. Readers
> might misinterpret this to mean that autovacuum will not process the
> partitions. There's a good definition of what the docs mean by
> "partitioned table" [0], but FWIW it took me some time before I
> consistently read "partitioned table" to mean "only the thing with relkind
> set to 'p'" and not "both the partitioned table and its partitions." So,
> while the current wording it technically correct, I think it'd be
> reasonable to expand it to help avoid confusion.
>
> 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.

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

Embrace your flaws. They make you human, rather than perfect,
which you will never be.