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@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

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