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Commit96030f9

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Don't call IS_DUMMY_REL() when cheapest_total_path might be junk.
Unlike the previous coding, this might result in a Gather per Appendsubplan when the target list is parallel-restricted, but such a planis probably worth considering in that case, since a single Gatheron top of the entire Append is impossible.Per Andres Freund and the buildfarm.Discussion:http://postgr.es/m/20180330050351.bmxx4cdtz67czjda@alap3.anarazel.de
1 parent681673e commit96030f9

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‎src/backend/optimizer/plan/planner.c‎

Lines changed: 17 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -1977,18 +1977,6 @@ grouping_planner(PlannerInfo *root, bool inheritance_update,
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scanjoin_targets_contain_srfs=NIL;
19781978
}
19791979

1980-
/*
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* If the final scan/join target is not parallel-safe, we must
1982-
* generate Gather paths now, since no partial paths will be generated
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* with the final scan/join targetlist. Otherwise, the Gather or
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* Gather Merge paths generated within apply_scanjoin_target_to_paths
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* will be superior to any we might generate now in that the
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* projection will be done in by each participant rather than only in
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* the leader.
1988-
*/
1989-
if (!scanjoin_target_parallel_safe)
1990-
generate_gather_paths(root,current_rel, false);
1991-
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/* Apply scan/join target. */
19931981
scanjoin_target_same_exprs=list_length(scanjoin_targets)==1
19941982
&&equal(scanjoin_target->exprs,current_rel->reltarget->exprs);
@@ -6817,15 +6805,29 @@ apply_scanjoin_target_to_paths(PlannerInfo *root,
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{
68186806
ListCell*lc;
68196807
PathTarget*scanjoin_target;
6808+
boolis_dummy_rel=IS_DUMMY_REL(rel);
68206809

68216810
check_stack_depth();
68226811

68236812
/*
6824-
* If the scan/join target is not parallel-safe,then the new partial
6825-
*pathlist is the empty list.
6813+
* If the scan/join target is not parallel-safe,partial paths cannot
6814+
*generate it.
68266815
*/
68276816
if (!scanjoin_target_parallel_safe)
68286817
{
6818+
/*
6819+
* Since we can't generate the final scan/join target, this is our
6820+
* last opportunity to use any partial paths that exist. We don't
6821+
* do this if the case where the target is parallel-safe, since we
6822+
* will be able to generate superior paths by doing it after the
6823+
* final scan/join target has been applied.
6824+
*
6825+
* Note that this may invalidate rel->cheapest_total_path, so we must
6826+
* not rely on it after this point without first calling set_cheapest.
6827+
*/
6828+
generate_gather_paths(root,rel, false);
6829+
6830+
/* Can't use parallel query above this level. */
68296831
rel->partial_pathlist=NIL;
68306832
rel->consider_parallel= false;
68316833
}
@@ -6840,7 +6842,7 @@ apply_scanjoin_target_to_paths(PlannerInfo *root,
68406842
rel->reltarget=llast_node(PathTarget,scanjoin_targets);
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68426844
/* Special case: handly dummy relations separately. */
6843-
if (IS_DUMMY_REL(rel))
6845+
if (is_dummy_rel)
68446846
{
68456847
/*
68466848
* Since this is a dummy rel, it's got a single Append path with no

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