Re: Add SPLIT PARTITION/MERGE PARTITIONS commands - Mailing list pgsql-hackers

From Pavel Borisov
Subject Re: Add SPLIT PARTITION/MERGE PARTITIONS commands
Date
Msg-id CALT9ZEHCDCXvg_=9oPb99mHzJPE=+N-DOodsuE20UorY35Jkzw@mail.gmail.com
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In response to Re: Add SPLIT PARTITION/MERGE PARTITIONS commands  (Alexander Korotkov <aekorotkov@gmail.com>)
Responses Re: Add SPLIT PARTITION/MERGE PARTITIONS commands
List pgsql-hackers
Hi, Alexander:

On Fri, 17 May 2024 at 14:05, Alexander Korotkov <aekorotkov@gmail.com> wrote:
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.
Thank you for working on this patch set!

Some minor things:
0001:
partition_split.sql
157 +-- Check that detection, that the new partition has the same name as one of
158 +-- the merged partitions, works correctly for temporary partitions 
Test for split with comment for merge. Maybe better something like:
"Split partition of a temporary table when one of the partitions after split has the same name as the partition being split"

0002: 
analgous -> analogous (maybe better using "like" instead of "analogous to")
heirarchy -> hierarchy

alter_table.sgml:
Maybe in documentation it's better not to provide reasoning, just state how it works: 
for consistency with <command>CREATE TABLE PARTITION OF</command> -> similar to <command>CREATE TABLE PARTITION OF</command>

Regards,
Pavel Borisov

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