Re: PG 14 release notes, first draft

On Tue, May 11, 2021 at 11:57:10AM +0900, Amit Langote wrote:
> On Mon, May 10, 2021 at 11:40 PM Justin Pryzby <pryzby@telsasoft.com> wrote:
> > Same as the last couple years, I checked for missing items in the release
> > notes, running something like this.
> >
> > git log --cherry-pick --oneline origin/REL_13_STABLE...origin/master
> >
> > Should any of these be included?
> >
> > 86dc90056d Rework planning and execution of UPDATE and DELETE.
> > a1115fa078 Postpone some more stuff out of ExecInitModifyTable.
> > c5b7ba4e67 Postpone some stuff out of ExecInitModifyTable.
> 
> I was just about to ask Bruce what he thinks about these.
> 
> To clarify, the first one is a big refactoring commit that allowed us
> to get rid of inheritance_planner(), a fairly inefficient way of
> planning updates/deletes on partitioned tables, especially when many
> partitions remain after pruning (or when pruning cannot be used).  One
> may see the performance of update/deletes, especially on partitioned
> tables, to be generally improved as a result of this commit, but maybe
> not as significantly as to be mentioned in E.1.3.1.1. Partitioning or
> even E.1.3.1.4. General Performance.  However, one user-visible
> feature that came out of this work is that updates/deletes can now use
> run-time pruning whereas they couldn't before.  Maybe that ought to be
> mentioned.  (This reminds me to send a patch to remove the note from
> 5.11.4. Partition Pruning that says that runtime pruning cannot be
> used for update/delete).
> 
> The other two commits can lead to improved performance of
> update/deletes when there are many unpruned partitions in the plan,
> but runtime pruning (a new feature as mentioned above) leads to only
> one or few partitions to actually be updated/deleted from.  I admit
> though that the cases for which performance has been improved still
> under-perform the cases that already performed better starting in v12,
> that is, the cases where the planner itself is able to trim down the
> plan to contain one or few partitions, so maybe nothing very big to
> see here just yet.  You may want to take a look at the benchmark
> results I had posted here:
> https://www.postgresql.org/message-id/CA%2BHiwqEcawatEaUh1uTbZMEZTJeLzbroRTz9_X9Z5CFjTWJkhw%40mail.gmail.com

Seems we might want to have a general release note item that mentions
improved update/delete performance for partitioned tables, yes?  I think
the run-time pruning and single-parition pullup are significant.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  If only the physical world exists, free will is an illusion.