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 <br...@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 <br...@momjian.us> https://momjian.us
EnterpriseDB https://enterprisedb.com
The usefulness of a cup is in its emptiness, Bruce Lee
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 <jda...@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>
