Date: Fri, 17 May 2019 11:36:53 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
Cc: David Rowley <david.rowley@2ndquadrant.com>,
	"Jonathan S. Katz" <jkatz@postgresql.org>,
	pgsql-advocacy@lists.postgresql.org
Subject: Re: PostgreSQL 12: Feature Highlights
Message-ID: <20190517153653.pmolnulev6imwsn3@momjian.us>
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On Fri, May 17, 2019 at 07:56:55PM +0900, Amit Langote wrote:
> On 2019/05/17 3:26, Bruce Momjian wrote:
> > I think the more specific we make the partition description, the more
> > limited it will appear to be.  I think almost all partition operations
> > will appear to be faster with PG 12, even if users can't articulate
> > exactly why.
> 
> I agree that the current description captures at a high level the many
> changes that made it possible.  Although, a couple of commits listed with
> this item don't have much to do with that description, AFAICT.  Especially
> 959d00e9d [1], which taught the planner to leverage the ordering imposed
> on partitions by range partitioning.  With that commit, getting ordered
> output from partitioned tables is now much quicker, especially with a
> LIMIT clause.  You can tell that it sounds clearly unrelated to the
> description we have now, which is "processing thousands of partitions is

Yes, it does.  I added this text and moved the commit item:

        Avoid sorting when partitions are already being scanned in the
        necessary order (David Rowley)

I certainly strugged to understand the maze of commits related to
partitioning.

> quicker when only small numbers of partitions are touched".  Some users of
> partitioning may not be interested in the use case described as vastly
> improved, but they may be delighted to hear about items such as the
> aforementioned commit.  Also, I suspect that the users whose use cases
> pushed them to use partitioning in the first place may also be the ones
> who do some of their own research about partitioning and eventually know
> many optimizations that are possible with it.  So, it's perhaps a good
> idea to let them know about such optimizations through release notes if
> it's the only place to put them, which I believe is the case with this
> particular item.  There are not that many commits to be taken out of the
> existing item and described separately, just this one I think.

Yes.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +