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Commitc651020

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Remove redundant PARTITION BY columns from WindowClauses
Here we adjust the query planner to have it remove items from a windowclause's PARTITION BY clause in cases where the pathkey for a column inthe PARTITION BY clause is redundant.Doing this allows the optimization added in9d9c02c to stop windowaggregation early rather than going into "pass-through" mode to findtuples belonging to the next partition. Also, when we manage to removeall PARTITION BY columns, we now no longer needlessly check that thecurrent tuple belongs to the same partition as the last tuple innodeWindowAgg.c. If the pathkey was redundant then all tuples mustcontain the same value for the given redundant column, so there's no pointin checking that during execution.Author: David RowleyReviewed-by: Richard GuoDiscussion:https://postgr.es/m/CAApHDvo2ji+hdxrxfXtRtsfSVw3to2o1nCO20qimw0dUGK8hcQ@mail.gmail.com
1 parent4637a6a commitc651020

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3 files changed

+46
-14
lines changed

3 files changed

+46
-14
lines changed

‎src/backend/optimizer/plan/createplan.c

Lines changed: 1 addition & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -2623,12 +2623,7 @@ create_windowagg_plan(PlannerInfo *root, WindowAggPath *best_path)
26232623

26242624
/*
26252625
* Convert SortGroupClause lists into arrays of attr indexes and equality
2626-
* operators, as wanted by executor. (Note: in principle, it's possible
2627-
* to drop some of the sort columns, if they were proved redundant by
2628-
* pathkey logic. However, it doesn't seem worth going out of our way to
2629-
* optimize such cases. In any case, we must *not* remove the ordering
2630-
* column for RANGE OFFSET cases, as the executor needs that for in_range
2631-
* tests even if it's known to be equal to some partitioning column.)
2626+
* operators, as wanted by executor.
26322627
*/
26332628
partColIdx= (AttrNumber*)palloc(sizeof(AttrNumber)*numPart);
26342629
partOperators= (Oid*)palloc(sizeof(Oid)*numPart);

‎src/backend/optimizer/plan/planner.c

Lines changed: 43 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -5999,6 +5999,9 @@ make_window_input_target(PlannerInfo *root,
59995999
*Create a pathkeys list describing the required input ordering
60006000
*for the given WindowClause.
60016001
*
6002+
* Modifies wc's partitionClause to remove any clauses which are deemed
6003+
* redundant by the pathkey logic.
6004+
*
60026005
* The required ordering is first the PARTITION keys, then the ORDER keys.
60036006
* In the future we might try to implement windowing using hashing, in which
60046007
* case the ordering could be relaxed, but for now we always sort.
@@ -6007,8 +6010,7 @@ static List *
60076010
make_pathkeys_for_window(PlannerInfo*root,WindowClause*wc,
60086011
List*tlist)
60096012
{
6010-
List*window_pathkeys;
6011-
List*window_sortclauses;
6013+
List*window_pathkeys=NIL;
60126014

60136015
/* Throw error if can't sort */
60146016
if (!grouping_is_sortable(wc->partitionClause))
@@ -6022,12 +6024,45 @@ make_pathkeys_for_window(PlannerInfo *root, WindowClause *wc,
60226024
errmsg("could not implement window ORDER BY"),
60236025
errdetail("Window ordering columns must be of sortable datatypes.")));
60246026

6025-
/* Okay, make the combined pathkeys */
6026-
window_sortclauses=list_concat_copy(wc->partitionClause,wc->orderClause);
6027-
window_pathkeys=make_pathkeys_for_sortclauses(root,
6028-
window_sortclauses,
6029-
tlist);
6030-
list_free(window_sortclauses);
6027+
/*
6028+
* First fetch the pathkeys for the PARTITION BY clause. We can safely
6029+
* remove any clauses from the wc->partitionClause for redundant pathkeys.
6030+
*/
6031+
if (wc->partitionClause!=NIL)
6032+
{
6033+
boolsortable;
6034+
6035+
window_pathkeys=make_pathkeys_for_sortclauses_extended(root,
6036+
&wc->partitionClause,
6037+
tlist,
6038+
true,
6039+
&sortable);
6040+
6041+
Assert(sortable);
6042+
}
6043+
6044+
/*
6045+
* In principle, we could also consider removing redundant ORDER BY items
6046+
* too as doing so does not alter the result of peer row checks done by
6047+
* the executor. However, we must *not* remove the ordering column for
6048+
* RANGE OFFSET cases, as the executor needs that for in_range tests even
6049+
* if it's known to be equal to some partitioning column.
6050+
*/
6051+
if (wc->orderClause!=NIL)
6052+
{
6053+
List*orderby_pathkeys;
6054+
6055+
orderby_pathkeys=make_pathkeys_for_sortclauses(root,
6056+
wc->orderClause,
6057+
tlist);
6058+
6059+
/* Okay, make the combined pathkeys */
6060+
if (window_pathkeys!=NIL)
6061+
window_pathkeys=append_pathkeys(window_pathkeys,orderby_pathkeys);
6062+
else
6063+
window_pathkeys=orderby_pathkeys;
6064+
}
6065+
60316066
returnwindow_pathkeys;
60326067
}
60336068

‎src/include/nodes/parsenodes.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1473,6 +1473,8 @@ typedef struct GroupingSet
14731473
* if the clause originally came from WINDOW, and is NULL if it originally
14741474
* was an OVER clause (but note that we collapse out duplicate OVERs).
14751475
* partitionClause and orderClause are lists of SortGroupClause structs.
1476+
* partitionClause is sanitized by the query planner to remove any columns or
1477+
* expressions belonging to redundant PathKeys.
14761478
* If we have RANGE with offset PRECEDING/FOLLOWING, the semantics of that are
14771479
* specified by startInRangeFunc/inRangeColl/inRangeAsc/inRangeNullsFirst
14781480
* for the start offset, or endInRangeFunc/inRange* for the end offset.

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