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Commit7c944bd

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Introduce a new GUC force_parallel_mode for testing purposes.
When force_parallel_mode = true, we enable the parallel mode restrictionsfor all queries for which this is believed to be safe. For the subset ofthose queries believed to be safe to run entirely within a worker, we spinup a worker and run the query there instead of running it in theoriginal process. When force_parallel_mode = regress, make additionalchanges to allow the regression tests to run cleanly even though parallelworkers have been injected under the hood.Taken together, this facilitates both better user testing and betterregression testing of the parallelism code.Robert Haas, with help from Amit Kapila and Rushabh Lathia.
1 parenta1c1af2 commit7c944bd

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13 files changed

+163
-20
lines changed

13 files changed

+163
-20
lines changed

‎doc/src/sgml/config.sgml‎

Lines changed: 45 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3802,6 +3802,51 @@ SELECT * FROM parent WHERE key = 2400;
38023802
</listitem>
38033803
</varlistentry>
38043804

3805+
<varlistentry id="guc-force-parallel-mode" xreflabel="force_parallel_mode">
3806+
<term><varname>force_parallel_mode</varname> (<type>enum</type>)
3807+
<indexterm>
3808+
<primary><varname>force_parallel_mode</> configuration parameter</primary>
3809+
</indexterm>
3810+
</term>
3811+
<listitem>
3812+
<para>
3813+
Allows the use of parallel queries for testing purposes even in cases
3814+
where no performance benefit is expected.
3815+
The allowed values of <varname>force_parallel_mode</> are
3816+
<literal>off</> (use parallel mode only when it is expected to improve
3817+
performance), <literal>on</> (force parallel query for all queries
3818+
for which it is thought to be safe), and <literal>regress</> (like
3819+
on, but with additional behavior changes to facilitate automated
3820+
regression testing).
3821+
</para>
3822+
3823+
<para>
3824+
More specifically, setting this value to <literal>on</> will add
3825+
a <literal>Gather</> node to the top of any query plan for which this
3826+
appears to be safe, so that the query runs inside of a parallel worker.
3827+
Even when a parallel worker is not available or cannot be used,
3828+
operations such as starting a subtransaction that would be prohibited
3829+
in a parallel query context will be prohibited unless the planner
3830+
believes that this will cause the query to fail. If failures or
3831+
unexpected results occur when this option is set, some functions used
3832+
by the query may need to be marked <literal>PARALLEL UNSAFE</literal>
3833+
(or, possibly, <literal>PARALLEL RESTRICTED</literal>).
3834+
</para>
3835+
3836+
<para>
3837+
Setting this value to <literal>regress</> has all of the same effects
3838+
as setting it to <literal>on</> plus some additional effect that are
3839+
intended to facilitate automated regression testing. Normally,
3840+
messages from a parallel worker are prefixed with a context line,
3841+
but a setting of <literal>regress</> suppresses this to guarantee
3842+
reproducible results. Also, the <literal>Gather</> nodes added to
3843+
plans by this setting are hidden from the <literal>EXPLAIN</> output
3844+
so that the output matches what would be obtained if this setting
3845+
were turned <literal>off</>.
3846+
</para>
3847+
</listitem>
3848+
</varlistentry>
3849+
38053850
</variablelist>
38063851
</sect2>
38073852
</sect1>

‎src/backend/access/transam/parallel.c‎

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -22,6 +22,7 @@
2222
#include"libpq/pqformat.h"
2323
#include"libpq/pqmq.h"
2424
#include"miscadmin.h"
25+
#include"optimizer/planmain.h"
2526
#include"storage/ipc.h"
2627
#include"storage/sinval.h"
2728
#include"storage/spin.h"
@@ -1079,7 +1080,8 @@ ParallelExtensionTrampoline(dsm_segment *seg, shm_toc *toc)
10791080
staticvoid
10801081
ParallelErrorContext(void*arg)
10811082
{
1082-
errcontext("parallel worker, PID %d",*(int32*)arg);
1083+
if (force_parallel_mode!=FORCE_PARALLEL_REGRESS)
1084+
errcontext("parallel worker, PID %d",*(int32*)arg);
10831085
}
10841086

10851087
/*

‎src/backend/commands/explain.c‎

Lines changed: 13 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -23,6 +23,7 @@
2323
#include"foreign/fdwapi.h"
2424
#include"nodes/nodeFuncs.h"
2525
#include"optimizer/clauses.h"
26+
#include"optimizer/planmain.h"
2627
#include"parser/parsetree.h"
2728
#include"rewrite/rewriteHandler.h"
2829
#include"tcop/tcopprot.h"
@@ -572,6 +573,7 @@ void
572573
ExplainPrintPlan(ExplainState*es,QueryDesc*queryDesc)
573574
{
574575
Bitmapset*rels_used=NULL;
576+
PlanState*ps;
575577

576578
Assert(queryDesc->plannedstmt!=NULL);
577579
es->pstmt=queryDesc->plannedstmt;
@@ -580,7 +582,17 @@ ExplainPrintPlan(ExplainState *es, QueryDesc *queryDesc)
580582
es->rtable_names=select_rtable_names_for_explain(es->rtable,rels_used);
581583
es->deparse_cxt=deparse_context_for_plan_rtable(es->rtable,
582584
es->rtable_names);
583-
ExplainNode(queryDesc->planstate,NIL,NULL,NULL,es);
585+
586+
/*
587+
* Sometimes we mark a Gather node as "invisible", which means that it's
588+
* not displayed in EXPLAIN output. The purpose of this is to allow
589+
* running regression tests with force_parallel_mode=regress to get the
590+
* same results as running the same tests with force_parallel_mode=off.
591+
*/
592+
ps=queryDesc->planstate;
593+
if (IsA(ps,GatherState)&&((Gather*)ps->plan)->invisible)
594+
ps=outerPlanState(ps);
595+
ExplainNode(ps,NIL,NULL,NULL,es);
584596
}
585597

586598
/*

‎src/backend/nodes/copyfuncs.c‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -334,6 +334,7 @@ _copyGather(const Gather *from)
334334
*/
335335
COPY_SCALAR_FIELD(num_workers);
336336
COPY_SCALAR_FIELD(single_copy);
337+
COPY_SCALAR_FIELD(invisible);
337338

338339
returnnewnode;
339340
}

‎src/backend/nodes/outfuncs.c‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -443,6 +443,7 @@ _outGather(StringInfo str, const Gather *node)
443443

444444
WRITE_INT_FIELD(num_workers);
445445
WRITE_BOOL_FIELD(single_copy);
446+
WRITE_BOOL_FIELD(invisible);
446447
}
447448

448449
staticvoid
@@ -1824,6 +1825,7 @@ _outPlannerGlobal(StringInfo str, const PlannerGlobal *node)
18241825
WRITE_BOOL_FIELD(hasRowSecurity);
18251826
WRITE_BOOL_FIELD(parallelModeOK);
18261827
WRITE_BOOL_FIELD(parallelModeNeeded);
1828+
WRITE_BOOL_FIELD(wholePlanParallelSafe);
18271829
WRITE_BOOL_FIELD(hasForeignJoin);
18281830
}
18291831

‎src/backend/nodes/readfuncs.c‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2053,6 +2053,7 @@ _readGather(void)
20532053

20542054
READ_INT_FIELD(num_workers);
20552055
READ_BOOL_FIELD(single_copy);
2056+
READ_BOOL_FIELD(invisible);
20562057

20572058
READ_DONE();
20582059
}

‎src/backend/optimizer/plan/createplan.c‎

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -212,6 +212,10 @@ create_plan(PlannerInfo *root, Path *best_path)
212212
/* Recursively process the path tree */
213213
plan=create_plan_recurse(root,best_path);
214214

215+
/* Update parallel safety information if needed. */
216+
if (!best_path->parallel_safe)
217+
root->glob->wholePlanParallelSafe= false;
218+
215219
/* Check we successfully assigned all NestLoopParams to plan nodes */
216220
if (root->curOuterParams!=NIL)
217221
elog(ERROR,"failed to assign all NestLoopParams to plan nodes");
@@ -4829,6 +4833,7 @@ make_gather(List *qptlist,
48294833
plan->righttree=NULL;
48304834
node->num_workers=nworkers;
48314835
node->single_copy=single_copy;
4836+
node->invisible= false;
48324837

48334838
returnnode;
48344839
}

‎src/backend/optimizer/plan/planner.c‎

Lines changed: 55 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -48,10 +48,12 @@
4848
#include"storage/dsm_impl.h"
4949
#include"utils/rel.h"
5050
#include"utils/selfuncs.h"
51+
#include"utils/syscache.h"
5152

5253

53-
/* GUCparameter */
54+
/* GUCparameters */
5455
doublecursor_tuple_fraction=DEFAULT_CURSOR_TUPLE_FRACTION;
56+
intforce_parallel_mode=FORCE_PARALLEL_OFF;
5557

5658
/* Hook for plugins to get control in planner() */
5759
planner_hook_typeplanner_hook=NULL;
@@ -230,25 +232,31 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
230232
!has_parallel_hazard((Node*)parse, true);
231233

232234
/*
233-
* glob->parallelModeOK should tell us whether it's necessary to impose
234-
* the parallel mode restrictions, but we don't actually want to impose
235-
* them unless we choose a parallel plan, so that people who mislabel
236-
* their functions but don't use parallelism anyway aren't harmed.
237-
* However, it's useful for testing purposes to be able to force the
238-
* restrictions to be imposed whenever a parallel plan is actually chosen
239-
* or not.
235+
* glob->parallelModeNeeded should tell us whether it's necessary to
236+
* impose the parallel mode restrictions, but we don't actually want to
237+
* impose them unless we choose a parallel plan, so that people who
238+
* mislabel their functions but don't use parallelism anyway aren't
239+
* harmed. But when force_parallel_mode is set, we enable the restrictions
240+
* whenever possible for testing purposes.
240241
*
241-
* (It's been suggested that we should always impose these restrictions
242-
* whenever glob->parallelModeOK is true, so that it's easier to notice
243-
* incorrectly-labeled functions sooner. That might be the right thing to
244-
* do, but for now I've taken this approach. We could also control this
245-
* with a GUC.)
242+
* glob->wholePlanParallelSafe should tell us whether it's OK to stick a
243+
* Gather node on top of the entire plan. However, it only needs to be
244+
* accurate when force_parallel_mode is 'on' or 'regress', so we don't
245+
* bother doing the work otherwise. The value we set here is just a
246+
* preliminary guess; it may get changed from true to false later, but
247+
* not visca versa.
246248
*/
247-
#ifdefFORCE_PARALLEL_MODE
248-
glob->parallelModeNeeded=glob->parallelModeOK;
249-
#else
250-
glob->parallelModeNeeded= false;
251-
#endif
249+
if (force_parallel_mode==FORCE_PARALLEL_OFF|| !glob->parallelModeOK)
250+
{
251+
glob->parallelModeNeeded= false;
252+
glob->wholePlanParallelSafe= false;/* either false or don't care */
253+
}
254+
else
255+
{
256+
glob->parallelModeNeeded= true;
257+
glob->wholePlanParallelSafe=
258+
!has_parallel_hazard((Node*)parse, false);
259+
}
252260

253261
/* Determine what fraction of the plan is likely to be scanned */
254262
if (cursorOptions&CURSOR_OPT_FAST_PLAN)
@@ -292,6 +300,35 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
292300
top_plan=materialize_finished_plan(top_plan);
293301
}
294302

303+
/*
304+
* At present, we don't copy subplans to workers. The presence of a
305+
* subplan in one part of the plan doesn't preclude the use of parallelism
306+
* in some other part of the plan, but it does preclude the possibility of
307+
* regarding the entire plan parallel-safe.
308+
*/
309+
if (glob->subplans!=NULL)
310+
glob->wholePlanParallelSafe= false;
311+
312+
/*
313+
* Optionally add a Gather node for testing purposes, provided this is
314+
* actually a safe thing to do.
315+
*/
316+
if (glob->wholePlanParallelSafe&&
317+
force_parallel_mode!=FORCE_PARALLEL_OFF)
318+
{
319+
Gather*gather=makeNode(Gather);
320+
321+
gather->plan.targetlist=top_plan->targetlist;
322+
gather->plan.qual=NIL;
323+
gather->plan.lefttree=top_plan;
324+
gather->plan.righttree=NULL;
325+
gather->num_workers=1;
326+
gather->single_copy= true;
327+
gather->invisible= (force_parallel_mode==FORCE_PARALLEL_REGRESS);
328+
root->glob->parallelModeNeeded= true;
329+
top_plan=&gather->plan;
330+
}
331+
295332
/*
296333
* If any Params were generated, run through the plan tree and compute
297334
* each plan node's extParam/allParam sets. Ideally we'd merge this into

‎src/backend/utils/misc/guc.c‎

Lines changed: 24 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -379,6 +379,19 @@ static const struct config_enum_entry huge_pages_options[] = {
379379
{NULL,0, false}
380380
};
381381

382+
staticconststructconfig_enum_entryforce_parallel_mode_options[]= {
383+
{"off",FORCE_PARALLEL_OFF, false},
384+
{"on",FORCE_PARALLEL_ON, false},
385+
{"regress",FORCE_PARALLEL_REGRESS, false},
386+
{"true",FORCE_PARALLEL_ON, true},
387+
{"false",FORCE_PARALLEL_OFF, true},
388+
{"yes",FORCE_PARALLEL_ON, true},
389+
{"no",FORCE_PARALLEL_OFF, true},
390+
{"1",FORCE_PARALLEL_ON, true},
391+
{"0",FORCE_PARALLEL_OFF, true},
392+
{NULL,0, false}
393+
};
394+
382395
/*
383396
* Options for enum values stored in other modules
384397
*/
@@ -863,6 +876,7 @@ static struct config_bool ConfigureNamesBool[] =
863876
true,
864877
NULL,NULL,NULL
865878
},
879+
866880
{
867881
{"geqo",PGC_USERSET,QUERY_TUNING_GEQO,
868882
gettext_noop("Enables genetic query optimization."),
@@ -3672,6 +3686,16 @@ static struct config_enum ConfigureNamesEnum[] =
36723686
NULL,NULL,NULL
36733687
},
36743688

3689+
{
3690+
{"force_parallel_mode",PGC_USERSET,QUERY_TUNING_OTHER,
3691+
gettext_noop("Forces use of parallel query facilities."),
3692+
gettext_noop("If possible, run query using a parallel worker and with parallel restrictions.")
3693+
},
3694+
&force_parallel_mode,
3695+
FORCE_PARALLEL_OFF,force_parallel_mode_options,
3696+
NULL,NULL,NULL
3697+
},
3698+
36753699
/* End-of-list marker */
36763700
{
36773701
{NULL,0,0,NULL,NULL},NULL,0,NULL,NULL,NULL,NULL

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

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -313,6 +313,7 @@
313313
#from_collapse_limit = 8
314314
#join_collapse_limit = 8# 1 disables collapsing of explicit
315315
# JOIN clauses
316+
#force_parallel_mode = off
316317

317318

318319
#------------------------------------------------------------------------------

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