Re: Add SPLIT PARTITION/MERGE PARTITIONS commands

On Tue, May 14, 2024 at 5:49 PM Justin Pryzby <pryzby@telsasoft.com> wrote:
> On Thu, May 09, 2024 at 12:51:32AM +0300, Alexander Korotkov wrote:
> > > > However, parent's table extended statistics already covers all its
> > > > children.
> > >
> > > => That's the wrong explanation.  It's not that "stats on the parent
> > > table cover its children".  It's that there are two types of stats:
> > > stats for the "table hierarchy" and stats for the individual table.
> > > That's true for single-column stats as well as for extended stats.
> > > In both cases, that's indicated by the inh flag in the code and in the
> > > catalog.
> > >
> > > The right explanation is that extended stats on partitioned tables are
> > > not similar to indexes.  Indexes on parent table are nothing other than
> > > a mechanism to create indexes on the child tables.  That's not true for
> > > stats.
> > >
> > > See also my prior messages
> > > ZiJW1g2nbQs9ekwK@pryzbyj2023
> > > Zi5Msg74C61DjJKW@pryzbyj2023
> >
> > Yes, I understand that parents pg_statistic entry with stainherit ==
> > true includes statistics for the children.  I tried to express this by
> > word "covers".  But you're right, this is the wrong explanation.
> >
> > Can I, please, ask you to revise the patch?
>
> I tried to make this clear but it'd be nice if someone (Tomas/Alvaro?)
> would check that this says what's wanted.

Thank you!

I've assembled the patches with the pending fixes.
0001 – The patch by Dmitry Koval for fixing detection of name
collision in SPLIT partition operation.  Also, I found that name
collision detection doesn't work well for MERGE partitions.  I've
added fix for that to this patch as well.
0002 -– Patch for skipping copy of extended statistics.  I would
appreciate more feedback about wording, but I'd like to get a correct
behavior into the source tree sooner.  If the docs and/or comments
need further improvements, we can fix that later.

I'm going to push both if no objections.