Re: First draft of the PG 15 release notes (sorting)

On Thu, May 12, 2022 at 10:38:42AM +1200, David Rowley wrote:
> On Wed, 11 May 2022 at 14:38, Justin Pryzby <pryzby@telsasoft.com> wrote:
> > I wonder if this is also relevant.
> >
> > 65014000b35 Replace polyphase merge algorithm with a simple balanced k-way merge.
> 
> Thanks for highlighting that. It very much is relevant. In fact, it
> seems to account for most of the 25% I mentioned.  That particular
> test was sorting 10 million tuples with 4MB of work_mem.
> 
> I think that "Improve sorting performance (Heikki Linnakangas)" should
> be moved out from "E.1.3.1.2. Indexes" and put below "E.1.3.1.4.
> General Performance"

Yes, good point, moved.

> The text likely should include the words "disk-based" so that it's
> clear that it's not the same as the other line about "in-memory
> sorts".  I'd also be open to just having a single line too. I'd vote
> to put Heikki's name first if we did that.
> 
> Maybe:
> 
> * Improve performance of sorting tuples (Heikki Linnakangas, Ronan
> Dunklau, David Rowley, Thomas Munro)
> 
> This improves the merging performance of individual on-disk sort
> batches, reduces memory consumption for in-memory sorts and reduces
> CPU overheads for certain in-memory sorts.

I kept separate entries:

    <!--
    Author: Heikki Linnakangas <heikki.linnakangas@iki.fi>
    2021-10-18 [65014000b] Replace polyphase merge algorithm with a simple balanced
    Author: Heikki Linnakangas <heikki.linnakangas@iki.fi>
    2021-10-25 [166f94377] Clarify the logic in a few places in the new balanced me
    -->
    
    <listitem>
    <para>
    Improve performance for sorts that exceed work_mem (Heikki Linnakangas)
    </para>
    
    <para>
    Specifically, switch to a batch sorting algorithm that uses more
    output streams internally.
    </para>
    </listitem>
    
    <!--
    Author: David Rowley <drowley@postgresql.org>
    2021-07-22 [91e9e89dc] Make nodeSort.c use Datum sorts for single column sorts
    Author: David Rowley <drowley@postgresql.org>
    2022-04-04 [40af10b57] Use Generation memory contexts to store tuples in sorts
    Author: John Naylor <john.naylor@postgresql.org>
    2022-04-02 [697492434] Specialize tuplesort routines for different kinds of abb
    -->
    
    <listitem>
    <para>
    Improve performance and reduce memory consumption of in-memory
    sorts (Ronan Dunklau, David Rowley, Thomas Munro)
    </para>
    </listitem>

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

  Indecision is a decision.  Inaction is an action.  Mark Batterson