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Date: Wed, 29 Jul 2020 21:30:50 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>,
	Masahiko Sawada <masahiko.sawada@2ndquadrant.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: PG 13 release notes, first draft
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On Wed, Jul 29, 2020 at 03:34:22PM -0700, Peter Geoghegan wrote:
> Hi Bruce,
> 
> On Fri, Jun 26, 2020 at 3:24 PM Bruce Momjian <bruce@momjian.us> wrote:
> > Patch attached and applied to PG 13.
> 
> I committed the hash_mem_multiplier GUC to Postgres 13 just now.
> 
> There should be a note about this in the Postgres 13 release notes,
> for the usual reasons. More importantly, the "Allow hash aggregation
> to use disk storage for large aggregation result sets" feature should
> reference the new GUC directly. Users should be advised that the GUC
> may be useful in cases where they upgrade and experience a performance
> regression linked to slower hash aggregation. Just including a
> documentation link for the GUC would be very helpful.

I came up with the attached patch.

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

  The usefulness of a cup is in its emptiness, Bruce Lee


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diff --git a/doc/src/sgml/release-13.sgml b/doc/src/sgml/release-13.sgml
new file mode 100644
index 18e6497..2586645
*** a/doc/src/sgml/release-13.sgml
--- b/doc/src/sgml/release-13.sgml
*************** Author: Jeff Davis <jdavis@postgresql.or
*** 649,655 ****
  
         <para>
          Previously, hash aggregation was avoided if it was expected to use
!         more than <xref linkend="guc-work-mem"/> memory.
         </para>
        </listitem>
  
--- 649,657 ----
  
         <para>
          Previously, hash aggregation was avoided if it was expected to use
!         more than <xref linkend="guc-work-mem"/> memory.  To use more
!         memory for hash query operations, increase <xref
!         linkend="guc-hash-mem-multiplier"/>.
         </para>
        </listitem>
  

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