Re: ANALYZE ONLY

On Mon, 23 Sept 2024 at 19:39, jian he <jian.universality@gmail.com> wrote:
> sql-analyze.html
> For partitioned tables, ANALYZE gathers statistics by sampling rows
> from all partitions. Each leaf partition is also recursively analyzed
> and the statistics updated. This recursive part may be disabled by
> using the ONLY keyword, otherwise, leaf partitions are analyzed only
> once, even with multi-level partitioning. No statistics are collected
> for only the parent table (without data from its partitions), because
> with partitioning it's guaranteed to be empty.
>
> allow me to ask anenglish language question.
> here "otherwise" means  specify ONLY or not?
> As far as i understand.
> if you specify ONLY, postgres will only do "For partitioned tables,
> ANALYZE gathers statistics by sampling rows from all partitions"
> if you not specify ONLY, postgres will do  "For partitioned tables,
> ANALYZE gathers statistics by sampling rows from all partitions *AND*
> also recursively analyze each leaf partition"
>
> Is my understanding correct?

The "Otherwise" case applies when "ONLY" isn't used.

If this is confusing, I think there's a bunch of detail that I tried
to keep that's just not that useful.  The part about analyzing
partitions just once and the part about not collecting non-inheritance
stats for the partitioned table seems like extra detail that's either
obvious or just not that important.

Can you have a look at the attached and let me know if it's easier to
understand now?

David