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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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11
src/backend/utils/misc/guc.c
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@ -2747,6 +2747,17 @@ static struct config_int ConfigureNamesInt[] =
NULL, NULL, NULL
},
{
{"min_parallel_relation_size", PGC_USERSET, QUERY_TUNING_COST,
gettext_noop("Sets the minimum size of relations to be considered for parallel scan."),
NULL,
GUC_UNIT_BLOCKS,
},
&min_parallel_relation_size,
1024, 0, INT_MAX / 3,
NULL, NULL, NULL
},
{
/* Can't be set in postgresql.conf */
{"server_version_num", PGC_INTERNAL, PRESET_OPTIONS,