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Invent min_parallel_relation_size GUC to replace a hard-wired constant.

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The main point of doing this is to allow the cutoff to be set very small,
even zero, to allow parallel-query behavior to be tested on relatively
small tables such as we typically use in the regression tests.  But it
might be of use to users too.  The number-of-workers scaling behavior in
create_plain_partial_paths() is pretty ad-hoc and subject to change, so
we won't expose anything about that, but the notion of not considering
parallel query at all for tables below size X seems reasonably stable.

Amit Kapila, per a suggestion from me

Discussion: <17170.1465830165@sss.pgh.pa.us>
This commit is contained in:
Tom Lane
2016-06-16 13:47:20 -04:00
parent 3b5a2a8856
commit 75be66464c
5 changed files with 37 additions and 5 deletions
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14
doc/src/sgml/config.sgml
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@ -3699,6 +3699,20 @@ include_dir 'conf.d'
</listitem>
</varlistentry>
<varlistentry id="guc-min-parallel-relation-size" xreflabel="min_parallel_relation_size">
<term><varname>min_parallel_relation_size</varname> (<type>integer</type>)
<indexterm>
<primary><varname>min_parallel_relation_size</> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
Sets the minimum size of relations to be considered for parallel scan.
The default is 8 megabytes (<literal>8MB</>).
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-effective-cache-size" xreflabel="effective_cache_size">
<term><varname>effective_cache_size</varname> (<type>integer</type>)
<indexterm>