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doc: PG 13 relnotes: hash_mem_multiplier can restore old behav. 

Document that hash_mem_multiplier can get query behavior closer to the
pre-PG 13 behavior of allowing hashing to use more memory.

Reported-by: Peter Geoghegan

Discussion: https://postgr.es/m/CAH2-Wzn3kwQm_pe6g2=ki+P7+ZRqH5GvFGn6SWfv_j7UUgcLdQ@mail.gmail.com

Backpatch-through: 13 only
This commit is contained in:
Bruce Momjian 2020-08-03 17:01:42 -04:00
parent 72ca61101a
commit e7a6cd5dcf
1 changed files with 4 additions and 1 deletions
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doc/src/sgml/release-13.sgml
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@ -649,7 +649,10 @@ Author: Jeff Davis <jdavis@postgresql.org>
<para>
Previously, hash aggregation was avoided if it was expected to use
more than <xref linkend="guc-work-mem"/> memory.
more than <xref linkend="guc-work-mem"/> memory. To reduce the
likelihood of using disk storage for hash aggregation and attain
behavior similar to previous Postgres releases, increase <xref
linkend="guc-hash-mem-multiplier"/>.
</para>
</listitem>