Daniel,
Thanks for the update.
On 07/25/2018 01:37 AM, Daniel Gustafsson wrote:
Hmm, this is missing the eqop fields of SortGroupClause. I haven't
tested yet but does the similar degradation happen if two
SortGroupCaluses have different eqop and the same other values?
I wasn’t able to construct a case showing this, but I also think you’re right.
Do you have an idea of a query that can trigger a regression? The attached
patch adds a stab at this, but I’m not sure if it’s the right approach.
To trigger that, in your test example you could order by empno::int8 for
one window, and by empno::int2 for another. But don't I think you have
to compare eqop here, because if eqop differs, sortop will differ too. I
removed the comparison from the patch. I also clarified (I hope) the
comments, and did the optimization I mentioned earlier: using array
instead of list for active clauses. Please see the attached v6.
Otherwise I think the patch is good.
--
Alexander Kuzmenkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
>From e6006da62d7d4c0c54750260e864e52e93e2dba9 Mon Sep 17 00:00:00 2001
From: Daniel Gustafsson <dan...@yesql.se>
Date: Tue, 12 Jun 2018 14:13:48 +0200
Subject: [PATCH] Order windows on partition/ordering prefix to reuse Sort
nodes
By ordering the Windows on partitioning/ordering prefix, the result
from Sort nodes can be reused by multiple WindowAgg nodes and thus
we can avoid Sort nodes.
---
src/backend/optimizer/plan/planner.c | 126 ++++++++++++++++++++++-------------
src/test/regress/expected/window.out | 60 +++++++++++++----
src/test/regress/sql/window.sql | 16 +++++
3 files changed, 144 insertions(+), 58 deletions(-)
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index df4ec44..299149f 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -110,6 +110,17 @@ typedef struct
int *tleref_to_colnum_map;
} grouping_sets_data;
+/*
+ * Temporary structure for use during WindowClause reordering in order to be
+ * be able to sort WindowClauses on partitioning/ordering prefix.
+ */
+typedef struct
+{
+ WindowClause *wc;
+ List *uniqueOrder; /* A List of unique ordering/partitioning
+ clauses per Window */
+} WindowClauseSortNode;
+
/* Local functions */
static Node *preprocess_expression(PlannerInfo *root, Node *expr, int kind);
static void preprocess_qual_conditions(PlannerInfo *root, Node *jtnode);
@@ -237,6 +248,7 @@ static void create_partitionwise_grouping_paths(PlannerInfo *root,
static bool group_by_has_partkey(RelOptInfo *input_rel,
List *targetList,
List *groupClause);
+static int common_prefix_cmp(const void *a, const void *b);
/*****************************************************************************
@@ -5253,68 +5265,92 @@ postprocess_setop_tlist(List *new_tlist, List *orig_tlist)
static List *
select_active_windows(PlannerInfo *root, WindowFuncLists *wflists)
{
- List *result;
- List *actives;
+ List *result = NIL;
ListCell *lc;
+ WindowClauseSortNode *actives = palloc(sizeof(WindowClauseSortNode)
+ * list_length(root->parse->windowClause));
+ int nActive = 0;
/* First, make a list of the active windows */
- actives = NIL;
- foreach(lc, root->parse->windowClause)
+ foreach (lc, root->parse->windowClause)
{
WindowClause *wc = lfirst_node(WindowClause, lc);
/* It's only active if wflists shows some related WindowFuncs */
Assert(wc->winref <= wflists->maxWinRef);
- if (wflists->windowFuncs[wc->winref] != NIL)
- actives = lappend(actives, wc);
+ if (wflists->windowFuncs[wc->winref] == NIL)
+ continue;
+
+ actives[nActive].wc = wc;
+ actives[nActive].uniqueOrder = list_concat_unique(
+ list_copy(wc->partitionClause), wc->orderClause);
+ nActive++;
}
/*
- * Now, ensure that windows with identical partitioning/ordering clauses
- * are adjacent in the list. This is required by the SQL standard, which
- * says that only one sort is to be used for such windows, even if they
- * are otherwise distinct (eg, different names or framing clauses).
- *
- * There is room to be much smarter here, for example detecting whether
- * one window's sort keys are a prefix of another's (so that sorting for
- * the latter would do for the former), or putting windows first that
- * match a sort order available for the underlying query. For the moment
- * we are content with meeting the spec.
- */
- result = NIL;
- while (actives != NIL)
- {
- WindowClause *wc = linitial_node(WindowClause, actives);
- ListCell *prev;
- ListCell *next;
-
- /* Move wc from actives to result */
- actives = list_delete_first(actives);
- result = lappend(result, wc);
-
- /* Now move any matching windows from actives to result */
- prev = NULL;
- for (lc = list_head(actives); lc; lc = next)
- {
- WindowClause *wc2 = lfirst_node(WindowClause, lc);
+ * Sort windows by their partitioning/ordering clauses, so that the windows
+ * that need the same sorting are adjacent in the list. This is required by
+ * the SQL standard, which says that only one sort is to be used for such
+ * windows, even if they are otherwise distinct (eg, different names or
+ * framing clauses). Additionally, if the entire list of clauses of one
+ * window is a prefix of another, put first the window with stronger sorting
+ * requirements. This way we will first sort for stronger window, and won't
+ * have to sort again for the weaker one.
+ */
+ qsort(actives, nActive, sizeof(WindowClauseSortNode), common_prefix_cmp);
- next = lnext(lc);
- /* framing options are NOT to be compared here! */
- if (equal(wc->partitionClause, wc2->partitionClause) &&
- equal(wc->orderClause, wc2->orderClause))
- {
- actives = list_delete_cell(actives, lc, prev);
- result = lappend(result, wc2);
- }
- else
- prev = lc;
- }
- }
+ for (; nActive > 0; nActive--)
+ result = lcons(actives[nActive - 1].wc, result);
+
+ pfree(actives);
return result;
}
/*
+ * common_prefix_cmp
+ * QSort comparison function for WindowClauseSortNodes
+ *
+ * Sort the windows by the required sorting clauses. First, compare the sort
+ * clauses themselves. Second, if one window's clauses are a prefix of another
+ * one's clauses, put the window with more sort clauses first.
+ */
+static int
+common_prefix_cmp(const void *a, const void *b)
+{
+ WindowClauseSortNode *wcsa = (WindowClauseSortNode *) a;
+ WindowClauseSortNode *wcsb = (WindowClauseSortNode *) b;
+ ListCell *item_a;
+ ListCell *item_b;
+
+ forboth(item_a, wcsa->uniqueOrder, item_b, wcsb->uniqueOrder)
+ {
+ SortGroupClause *sca = lfirst(item_a);
+ SortGroupClause *scb = lfirst(item_b);
+
+ if (sca->tleSortGroupRef > scb->tleSortGroupRef)
+ return -1;
+ else if (sca->tleSortGroupRef < scb->tleSortGroupRef)
+ return 1;
+ else if (sca->sortop > scb->sortop)
+ return -1;
+ else if (sca->sortop < scb->sortop)
+ return 1;
+ else if (sca->nulls_first && !scb->nulls_first)
+ return -1;
+ else if (!sca->nulls_first && scb->nulls_first)
+ return 1;
+ }
+
+ if (list_length(wcsa->uniqueOrder) > list_length(wcsb->uniqueOrder))
+ return -1;
+ else if (list_length(wcsa->uniqueOrder) < list_length(wcsb->uniqueOrder))
+ return 1;
+
+ return 0;
+}
+
+/*
* make_window_input_target
* Generate appropriate PathTarget for initial input to WindowAgg nodes.
*
diff --git a/src/test/regress/expected/window.out b/src/test/regress/expected/window.out
index 562006a..662d348 100644
--- a/src/test/regress/expected/window.out
+++ b/src/test/regress/expected/window.out
@@ -504,9 +504,9 @@ SELECT sum(salary),
FROM empsalary GROUP BY depname;
sum | row_number | sum
-------+------------+-------
- 14600 | 3 | 14600
- 7400 | 2 | 22000
25100 | 1 | 47100
+ 7400 | 2 | 22000
+ 14600 | 3 | 14600
(3 rows)
-- identical windows with different names
@@ -2994,9 +2994,9 @@ SELECT sum(salary), row_number() OVER (ORDER BY depname), sum(
FROM empsalary GROUP BY depname;
sum | row_number | filtered_sum | depname
-------+------------+--------------+-----------
- 14600 | 3 | | sales
- 7400 | 2 | 3500 | personnel
25100 | 1 | 22600 | develop
+ 7400 | 2 | 3500 | personnel
+ 14600 | 3 | | sales
(3 rows)
-- Test pushdown of quals into a subquery containing window functions
@@ -3008,13 +3008,13 @@ SELECT * FROM
min(salary) OVER (PARTITION BY depname || 'A', depname) depminsalary
FROM empsalary) emp
WHERE depname = 'sales';
- QUERY PLAN
----------------------------------------------------------------------
+ QUERY PLAN
+--------------------------------------------------------------------------
Subquery Scan on emp
-> WindowAgg
- -> Sort
- Sort Key: (((empsalary.depname)::text || 'A'::text))
- -> WindowAgg
+ -> WindowAgg
+ -> Sort
+ Sort Key: (((empsalary.depname)::text || 'A'::text))
-> Seq Scan on empsalary
Filter: ((depname)::text = 'sales'::text)
(7 rows)
@@ -3027,19 +3027,53 @@ SELECT * FROM
min(salary) OVER (PARTITION BY depname) depminsalary
FROM empsalary) emp
WHERE depname = 'sales';
- QUERY PLAN
------------------------------------------------------------
+ QUERY PLAN
+-------------------------------------------------------
Subquery Scan on emp
Filter: ((emp.depname)::text = 'sales'::text)
-> WindowAgg
-> Sort
- Sort Key: empsalary.depname
+ Sort Key: empsalary.enroll_date
-> WindowAgg
-> Sort
- Sort Key: empsalary.enroll_date
+ Sort Key: empsalary.depname
-> Seq Scan on empsalary
(9 rows)
+-- Test Sort node collapsing
+EXPLAIN (COSTS OFF)
+SELECT * FROM
+ (SELECT depname,
+ sum(salary) OVER (PARTITION BY depname order by empno) depsalary,
+ min(salary) OVER (PARTITION BY depname, empno order by enroll_date) depminsalary
+ FROM empsalary) emp
+WHERE depname = 'sales';
+ QUERY PLAN
+----------------------------------------------------------------------
+ Subquery Scan on emp
+ -> WindowAgg
+ -> WindowAgg
+ -> Sort
+ Sort Key: empsalary.empno, empsalary.enroll_date
+ -> Seq Scan on empsalary
+ Filter: ((depname)::text = 'sales'::text)
+(7 rows)
+
+-- Test Sort node reordering
+EXPLAIN (COSTS OFF)
+SELECT
+ lead(1) OVER (PARTITION BY depname ORDER BY salary, enroll_date),
+ lag(1) OVER (PARTITION BY depname ORDER BY salary,enroll_date,empno)
+FROM empsalary;
+ QUERY PLAN
+-------------------------------------------------------------
+ WindowAgg
+ -> WindowAgg
+ -> Sort
+ Sort Key: depname, salary, enroll_date, empno
+ -> Seq Scan on empsalary
+(5 rows)
+
-- cleanup
DROP TABLE empsalary;
-- test user-defined window function with named args and default args
diff --git a/src/test/regress/sql/window.sql b/src/test/regress/sql/window.sql
index e2943a3..fc6d4cc 100644
--- a/src/test/regress/sql/window.sql
+++ b/src/test/regress/sql/window.sql
@@ -892,6 +892,22 @@ SELECT * FROM
FROM empsalary) emp
WHERE depname = 'sales';
+-- Test Sort node collapsing
+EXPLAIN (COSTS OFF)
+SELECT * FROM
+ (SELECT depname,
+ sum(salary) OVER (PARTITION BY depname order by empno) depsalary,
+ min(salary) OVER (PARTITION BY depname, empno order by enroll_date) depminsalary
+ FROM empsalary) emp
+WHERE depname = 'sales';
+
+-- Test Sort node reordering
+EXPLAIN (COSTS OFF)
+SELECT
+ lead(1) OVER (PARTITION BY depname ORDER BY salary, enroll_date),
+ lag(1) OVER (PARTITION BY depname ORDER BY salary,enroll_date,empno)
+FROM empsalary;
+
-- cleanup
DROP TABLE empsalary;
--
2.7.4
