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Commit75be664

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Invent min_parallel_relation_size GUC to replace a hard-wired constant.
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 relativelysmall tables such as we typically use in the regression tests. But itmight be of use to users too. The number-of-workers scaling behavior increate_plain_partial_paths() is pretty ad-hoc and subject to change, sowe won't expose anything about that, but the notion of not consideringparallel query at all for tables below size X seems reasonably stable.Amit Kapila, per a suggestion from meDiscussion: <17170.1465830165@sss.pgh.pa.us>
1 parent3b5a2a8 commit75be664

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5 files changed

+37
-5
lines changed

5 files changed

+37
-5
lines changed

‎doc/src/sgml/config.sgml

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@@ -3699,6 +3699,20 @@ include_dir 'conf.d'
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</listitem>
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</varlistentry>
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<varlistentry id="guc-min-parallel-relation-size" xreflabel="min_parallel_relation_size">
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<term><varname>min_parallel_relation_size</varname> (<type>integer</type>)
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<indexterm>
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<primary><varname>min_parallel_relation_size</> configuration parameter</primary>
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</indexterm>
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</term>
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<listitem>
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<para>
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Sets the minimum size of relations to be considered for parallel scan.
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The default is 8 megabytes (<literal>8MB</>).
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</para>
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</listitem>
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</varlistentry>
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<varlistentry id="guc-effective-cache-size" xreflabel="effective_cache_size">
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<term><varname>effective_cache_size</varname> (<type>integer</type>)
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<indexterm>

‎src/backend/optimizer/path/allpaths.c

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@@ -15,6 +15,7 @@
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#include"postgres.h"
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#include<limits.h>
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#include<math.h>
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#include"access/sysattr.h"
@@ -56,6 +57,7 @@ typedef struct pushdown_safety_info
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/* These parameters are set by GUC */
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boolenable_geqo= false;/* just in case GUC doesn't set it */
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intgeqo_threshold;
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intmin_parallel_relation_size;
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/* Hook for plugins to get control in set_rel_pathlist() */
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set_rel_pathlist_hook_typeset_rel_pathlist_hook=NULL;
@@ -690,7 +692,7 @@ create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel)
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parallel_workers=rel->rel_parallel_workers;
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else
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{
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intparallel_threshold=1000;
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intparallel_threshold;
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/*
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* If this relation is too small to be worth a parallel scan, just
@@ -699,21 +701,24 @@ create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel)
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* might not be worthwhile just for this relation, but when combined
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* with all of its inheritance siblings it may well pay off.
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*/
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if (rel->pages<parallel_threshold&&
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if (rel->pages<(BlockNumber)min_parallel_relation_size&&
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rel->reloptkind==RELOPT_BASEREL)
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return;
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/*
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* Select the number of workers based on the log of the size of the
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* relation. This probably needs to be a good deal more
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* sophisticated, but we need something here for now.
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* sophisticated, but we need something here for now. Note that the
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* upper limit of the min_parallel_relation_size GUC is chosen to
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* prevent overflow here.
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*/
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parallel_workers=1;
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while (rel->pages>parallel_threshold*3)
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parallel_threshold=Max(min_parallel_relation_size,1);
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while (rel->pages >= (BlockNumber) (parallel_threshold*3))
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{
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parallel_workers++;
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parallel_threshold *=3;
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if (parallel_threshold >=PG_INT32_MAX /3)
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if (parallel_threshold>INT_MAX /3)
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break;/* avoid overflow */
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}
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}

‎src/backend/utils/misc/guc.c

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

‎src/backend/utils/misc/postgresql.conf.sample

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@@ -304,6 +304,7 @@
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#cpu_operator_cost = 0.0025# same scale as above
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#parallel_tuple_cost = 0.1# same scale as above
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#parallel_setup_cost = 1000.0# same scale as above
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#min_parallel_relation_size = 8MB
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#effective_cache_size = 4GB
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# - Genetic Query Optimizer -

‎src/include/optimizer/paths.h

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@@ -22,6 +22,7 @@
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*/
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externboolenable_geqo;
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externintgeqo_threshold;
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externintmin_parallel_relation_size;
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/* Hook for plugins to get control in set_rel_pathlist() */
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typedefvoid (*set_rel_pathlist_hook_type) (PlannerInfo*root,

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