Re: pg_class.relpages documentation does not mention relpages corner case

On Mon, Jun 5, 2023 at 11:03:49PM +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
>
> Page: https://www.postgresql.org/docs/14/catalog-pg-class.html
> Description:
>
> In the pg_class documentation [1], the relpages column is described as
>
> >Size of the on-disk representation of this table in pages (of size BLCKSZ).
> This is only an estimate used by the planner. It is updated by VACUUM,
> ANALYZE, and a few DDL commands such as CREATE INDEX.
>
> However, it looks like this is -1 for partitioned tables. At least for ones
> that have children and have been analyze since adding a child partition, it
> seems. I'm not sure how to word that concisely, but should the documentation
> note this case? Or can this just be zero for partitioned tales? I'm not sure
> if it's too late for that, but they don't actually have any relpages, so it
> seems odd that they need a sentinel value.

Uh, there are discussions about needing to run ANALYZE on partitioned
tables, so in those cases the statistics would be cumulative of all
partitions:

https://www.postgresql.org/message-id/20230112232747.GA2111950@nathanxps13

If we set the relpages to zero, that would not be reflecting the
partitions. I feel -1 is probably the best unless we want to put the
total of all partitions in there, but that would be confusing too.

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

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