From 254f96967188123851f4324d46d30c36e6637edd Mon Sep 17 00:00:00 2001
From: amit <amitlangote09@gmail.com>
Date: Mon, 6 Feb 2017 17:26:48 +0900
Subject: [PATCH 3/3] Avoid creating scan nodes for partitioned tables

Currently, we create scan nodes for inheritance parents in their role
as an inheritance set member.  Partitioned tables do not contain any
data, so it's useless to create scan nodes for them.  So we need not
create AppendRelInfo's for them in the planner prep phase.

Further, the planner prep phase turns off inheritance on the parent RTE
if there isn't at least one child member (other than the parent itself
which in normal cases is also a child member), which means the latter
phases will not consider creating an Append plan and instead create a
scan node. Avoid this if the RTE is a partitioned table, by noticing
such cases in set_rel_size().  Per suggestion from Ashutosh Bapat.

Next, since we do not add the RTE corresponding to the root partitioned
table as the 1st child member of the inheritance set, inheritance_planner()
must not assume the same when assigning nominalRelation to a ModifyTable
node.
---
 src/backend/optimizer/path/allpaths.c  |   9 +++
 src/backend/optimizer/plan/planner.c   |  16 ++++-
 src/backend/optimizer/prep/prepunion.c |  19 +++++-
 src/test/regress/expected/inherit.out  | 116 +++++++++------------------------
 src/test/regress/sql/inherit.sql       |   4 ++
 5 files changed, 76 insertions(+), 88 deletions(-)

diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 633b5c1608..759e14d5fe 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -342,6 +342,15 @@ set_rel_size(PlannerInfo *root, RelOptInfo *rel,
 					/* Foreign table */
 					set_foreign_size(root, rel, rte);
 				}
+				else if (rte->relkind == RELKIND_PARTITIONED_TABLE)
+				{
+					/*
+					 * An empty partitioned table, i.e., one without any leaf
+					 * partitions, as signaled by rte->inh being set to false
+					 * by the prep phase (see expand_inherited_rtentry).
+					 */
+					set_dummy_rel_pathlist(rel);
+				}
 				else if (rte->tablesample != NULL)
 				{
 					/* Sampled relation */
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index ca0ae7883e..9918d2ba8c 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -996,10 +996,20 @@ inheritance_planner(PlannerInfo *root)
 	RelOptInfo *final_rel;
 	ListCell   *lc;
 	Index		rti;
+	RangeTblEntry *parent_rte;
 
 	Assert(parse->commandType != CMD_INSERT);
 
 	/*
+	 * If the parent RTE is a partitioned table, we should use that as the
+	 * nominal relation, because we do not have the duplicate parent RTE,
+	 * unlike in the case of a non-partitioned inheritance parent.
+	 */
+	parent_rte = rt_fetch(parentRTindex, root->parse->rtable);
+	if (parent_rte->relkind == RELKIND_PARTITIONED_TABLE)
+		nominalRelation = parentRTindex;
+
+	/*
 	 * We generate a modified instance of the original Query for each target
 	 * relation, plan that, and put all the plans into a list that will be
 	 * controlled by a single ModifyTable node.  All the instances share the
@@ -1060,7 +1070,6 @@ inheritance_planner(PlannerInfo *root)
 	{
 		AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(lc);
 		PlannerInfo *subroot;
-		RangeTblEntry *parent_rte;
 		RangeTblEntry *child_rte;
 		RelOptInfo *sub_final_rel;
 		Path	   *subpath;
@@ -1214,6 +1223,11 @@ inheritance_planner(PlannerInfo *root)
 		 * will not be otherwise referenced in the plan, doing so would give
 		 * rise to confusing use of multiple aliases in EXPLAIN output for
 		 * what the user will think is the "same" table.)
+		 *
+		 * If the parent is a partitioned table, we do not have a separate RTE
+		 * representing it as a member of the inheritance set, because we do
+		 * not create a scan plan for it.  As mentioned at the top of this
+		 * function, we make the parent RTE itself the nominal relation.
 		 */
 		if (nominalRelation < 0)
 			nominalRelation = appinfo->child_relid;
diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c
index 1389db18ba..78f51c762b 100644
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -1450,6 +1450,18 @@ expand_inherited_rtentry(PlannerInfo *root, RangeTblEntry *rte, Index rti)
 			newrelation = oldrelation;
 
 		/*
+		 * Ignore partitioned tables here, because we do not want them to
+		 * be considered as child tables in the inheritance set.  No scan
+		 * plans will be created for them.
+		 */
+		if (newrelation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+		{
+			if (newrelation != oldrelation)
+				heap_close(newrelation, lockmode);
+			continue;
+		}
+
+		/*
 		 * It is possible that the parent table has children that are temp
 		 * tables of other backends.  We cannot safely access such tables
 		 * (because of buffering issues), and the best thing to do seems to be
@@ -1548,9 +1560,12 @@ expand_inherited_rtentry(PlannerInfo *root, RangeTblEntry *rte, Index rti)
 	 * If all the children were temp tables, pretend it's a non-inheritance
 	 * situation.  The duplicate RTE we added for the parent table is
 	 * harmless, so we don't bother to get rid of it; ditto for the useless
-	 * PlanRowMark node.
+	 * PlanRowMark node.  Since we do not create appinfos for partitioned
+	 * tables above, we may end up with just one appinfo corresponding to
+	 * the only leaf partition, which is fine.
 	 */
-	if (list_length(appinfos) < 2)
+	if ((rte->relkind != RELKIND_PARTITIONED_TABLE &&
+		 list_length(appinfos) < 2) || list_length(appinfos) < 1)
 	{
 		/* Clear flag before returning */
 		rte->inh = false;
diff --git a/src/test/regress/expected/inherit.out b/src/test/regress/expected/inherit.out
index a8c8b28a75..cd33a1a7ec 100644
--- a/src/test/regress/expected/inherit.out
+++ b/src/test/regress/expected/inherit.out
@@ -1598,6 +1598,14 @@ reset enable_bitmapscan;
 create table list_parted (
 	a	varchar
 ) partition by list (a);
+-- test scanning partitioned table without any partitions
+explain (costs off) select * from list_parted;
+        QUERY PLAN        
+--------------------------
+ Result
+   One-Time Filter: false
+(2 rows)
+
 create table part_ab_cd partition of list_parted for values in ('ab', 'cd');
 create table part_ef_gh partition of list_parted for values in ('ef', 'gh');
 create table part_null_xy partition of list_parted for values in (null, 'xy');
@@ -1605,71 +1613,60 @@ explain (costs off) select * from list_parted;
            QUERY PLAN           
 --------------------------------
  Append
-   ->  Seq Scan on list_parted
    ->  Seq Scan on part_ab_cd
    ->  Seq Scan on part_ef_gh
    ->  Seq Scan on part_null_xy
-(5 rows)
+(4 rows)
 
 explain (costs off) select * from list_parted where a is null;
            QUERY PLAN           
 --------------------------------
  Append
-   ->  Seq Scan on list_parted
-         Filter: (a IS NULL)
    ->  Seq Scan on part_null_xy
          Filter: (a IS NULL)
-(5 rows)
+(3 rows)
 
 explain (costs off) select * from list_parted where a is not null;
            QUERY PLAN            
 ---------------------------------
  Append
-   ->  Seq Scan on list_parted
-         Filter: (a IS NOT NULL)
    ->  Seq Scan on part_ab_cd
          Filter: (a IS NOT NULL)
    ->  Seq Scan on part_ef_gh
          Filter: (a IS NOT NULL)
    ->  Seq Scan on part_null_xy
          Filter: (a IS NOT NULL)
-(9 rows)
+(7 rows)
 
 explain (costs off) select * from list_parted where a in ('ab', 'cd', 'ef');
                         QUERY PLAN                        
 ----------------------------------------------------------
  Append
-   ->  Seq Scan on list_parted
-         Filter: ((a)::text = ANY ('{ab,cd,ef}'::text[]))
    ->  Seq Scan on part_ab_cd
          Filter: ((a)::text = ANY ('{ab,cd,ef}'::text[]))
    ->  Seq Scan on part_ef_gh
          Filter: ((a)::text = ANY ('{ab,cd,ef}'::text[]))
-(7 rows)
+(5 rows)
 
 explain (costs off) select * from list_parted where a = 'ab' or a in (null, 'cd');
                                       QUERY PLAN                                       
 ---------------------------------------------------------------------------------------
  Append
-   ->  Seq Scan on list_parted
-         Filter: (((a)::text = 'ab'::text) OR ((a)::text = ANY ('{NULL,cd}'::text[])))
    ->  Seq Scan on part_ab_cd
          Filter: (((a)::text = 'ab'::text) OR ((a)::text = ANY ('{NULL,cd}'::text[])))
    ->  Seq Scan on part_ef_gh
          Filter: (((a)::text = 'ab'::text) OR ((a)::text = ANY ('{NULL,cd}'::text[])))
    ->  Seq Scan on part_null_xy
          Filter: (((a)::text = 'ab'::text) OR ((a)::text = ANY ('{NULL,cd}'::text[])))
-(9 rows)
+(7 rows)
 
 explain (costs off) select * from list_parted where a = 'ab';
                 QUERY PLAN                
 ------------------------------------------
  Append
-   ->  Seq Scan on list_parted
-         Filter: ((a)::text = 'ab'::text)
    ->  Seq Scan on part_ab_cd
          Filter: ((a)::text = 'ab'::text)
-(5 rows)
+(3 rows)
 
 create table range_list_parted (
 	a	int,
@@ -1689,14 +1686,9 @@ create table part_40_inf_ab partition of part_40_inf for values in ('ab');
 create table part_40_inf_cd partition of part_40_inf for values in ('cd');
 create table part_40_inf_null partition of part_40_inf for values in (null);
 explain (costs off) select * from range_list_parted;
-             QUERY PLAN              
--------------------------------------
+             QUERY PLAN             
+------------------------------------
  Append
-   ->  Seq Scan on range_list_parted
-   ->  Seq Scan on part_1_10
-   ->  Seq Scan on part_10_20
-   ->  Seq Scan on part_21_30
-   ->  Seq Scan on part_40_inf
    ->  Seq Scan on part_1_10_ab
    ->  Seq Scan on part_1_10_cd
    ->  Seq Scan on part_10_20_ab
@@ -1706,36 +1698,22 @@ explain (costs off) select * from range_list_parted;
    ->  Seq Scan on part_40_inf_ab
    ->  Seq Scan on part_40_inf_cd
    ->  Seq Scan on part_40_inf_null
-(15 rows)
+(10 rows)
 
 explain (costs off) select * from range_list_parted where a = 5;
-             QUERY PLAN              
--------------------------------------
+           QUERY PLAN           
+--------------------------------
  Append
-   ->  Seq Scan on range_list_parted
-         Filter: (a = 5)
-   ->  Seq Scan on part_1_10
-         Filter: (a = 5)
    ->  Seq Scan on part_1_10_ab
          Filter: (a = 5)
    ->  Seq Scan on part_1_10_cd
          Filter: (a = 5)
-(9 rows)
+(5 rows)
 
 explain (costs off) select * from range_list_parted where b = 'ab';
-             QUERY PLAN              
--------------------------------------
+             QUERY PLAN             
+------------------------------------
  Append
-   ->  Seq Scan on range_list_parted
-         Filter: (b = 'ab'::bpchar)
-   ->  Seq Scan on part_1_10
-         Filter: (b = 'ab'::bpchar)
-   ->  Seq Scan on part_10_20
-         Filter: (b = 'ab'::bpchar)
-   ->  Seq Scan on part_21_30
-         Filter: (b = 'ab'::bpchar)
-   ->  Seq Scan on part_40_inf
-         Filter: (b = 'ab'::bpchar)
    ->  Seq Scan on part_1_10_ab
          Filter: (b = 'ab'::bpchar)
    ->  Seq Scan on part_10_20_ab
@@ -1744,27 +1722,19 @@ explain (costs off) select * from range_list_parted where b = 'ab';
          Filter: (b = 'ab'::bpchar)
    ->  Seq Scan on part_40_inf_ab
          Filter: (b = 'ab'::bpchar)
-(19 rows)
+(9 rows)
 
 explain (costs off) select * from range_list_parted where a between 3 and 23 and b in ('ab');
                            QUERY PLAN                            
 -----------------------------------------------------------------
  Append
-   ->  Seq Scan on range_list_parted
-         Filter: ((a >= 3) AND (a <= 23) AND (b = 'ab'::bpchar))
-   ->  Seq Scan on part_1_10
-         Filter: ((a >= 3) AND (a <= 23) AND (b = 'ab'::bpchar))
-   ->  Seq Scan on part_10_20
-         Filter: ((a >= 3) AND (a <= 23) AND (b = 'ab'::bpchar))
-   ->  Seq Scan on part_21_30
-         Filter: ((a >= 3) AND (a <= 23) AND (b = 'ab'::bpchar))
    ->  Seq Scan on part_1_10_ab
          Filter: ((a >= 3) AND (a <= 23) AND (b = 'ab'::bpchar))
    ->  Seq Scan on part_10_20_ab
          Filter: ((a >= 3) AND (a <= 23) AND (b = 'ab'::bpchar))
    ->  Seq Scan on part_21_30_ab
          Filter: ((a >= 3) AND (a <= 23) AND (b = 'ab'::bpchar))
-(15 rows)
+(7 rows)
 
 /* Should select no rows because range partition key cannot be null */
 explain (costs off) select * from range_list_parted where a is null;
@@ -1776,37 +1746,17 @@ explain (costs off) select * from range_list_parted where a is null;
 
 /* Should only select rows from the null-accepting partition */
 explain (costs off) select * from range_list_parted where b is null;
-             QUERY PLAN              
--------------------------------------
+             QUERY PLAN             
+------------------------------------
  Append
-   ->  Seq Scan on range_list_parted
-         Filter: (b IS NULL)
-   ->  Seq Scan on part_1_10
-         Filter: (b IS NULL)
-   ->  Seq Scan on part_10_20
-         Filter: (b IS NULL)
-   ->  Seq Scan on part_21_30
-         Filter: (b IS NULL)
-   ->  Seq Scan on part_40_inf
-         Filter: (b IS NULL)
    ->  Seq Scan on part_40_inf_null
          Filter: (b IS NULL)
-(13 rows)
+(3 rows)
 
 explain (costs off) select * from range_list_parted where a is not null and a < 67;
                    QUERY PLAN                   
 ------------------------------------------------
  Append
-   ->  Seq Scan on range_list_parted
-         Filter: ((a IS NOT NULL) AND (a < 67))
-   ->  Seq Scan on part_1_10
-         Filter: ((a IS NOT NULL) AND (a < 67))
-   ->  Seq Scan on part_10_20
-         Filter: ((a IS NOT NULL) AND (a < 67))
-   ->  Seq Scan on part_21_30
-         Filter: ((a IS NOT NULL) AND (a < 67))
-   ->  Seq Scan on part_40_inf
-         Filter: ((a IS NOT NULL) AND (a < 67))
    ->  Seq Scan on part_1_10_ab
          Filter: ((a IS NOT NULL) AND (a < 67))
    ->  Seq Scan on part_1_10_cd
@@ -1825,23 +1775,19 @@ explain (costs off) select * from range_list_parted where a is not null and a <
          Filter: ((a IS NOT NULL) AND (a < 67))
    ->  Seq Scan on part_40_inf_null
          Filter: ((a IS NOT NULL) AND (a < 67))
-(29 rows)
+(19 rows)
 
 explain (costs off) select * from range_list_parted where a >= 30;
-             QUERY PLAN              
--------------------------------------
+             QUERY PLAN             
+------------------------------------
  Append
-   ->  Seq Scan on range_list_parted
-         Filter: (a >= 30)
-   ->  Seq Scan on part_40_inf
-         Filter: (a >= 30)
    ->  Seq Scan on part_40_inf_ab
          Filter: (a >= 30)
    ->  Seq Scan on part_40_inf_cd
          Filter: (a >= 30)
    ->  Seq Scan on part_40_inf_null
          Filter: (a >= 30)
-(11 rows)
+(7 rows)
 
 drop table list_parted cascade;
 NOTICE:  drop cascades to 3 other objects
diff --git a/src/test/regress/sql/inherit.sql b/src/test/regress/sql/inherit.sql
index a8b7eb1c8d..34274746d3 100644
--- a/src/test/regress/sql/inherit.sql
+++ b/src/test/regress/sql/inherit.sql
@@ -570,6 +570,10 @@ reset enable_bitmapscan;
 create table list_parted (
 	a	varchar
 ) partition by list (a);
+
+-- test scanning partitioned table without any partitions
+explain (costs off) select * from list_parted;
+
 create table part_ab_cd partition of list_parted for values in ('ab', 'cd');
 create table part_ef_gh partition of list_parted for values in ('ef', 'gh');
 create table part_null_xy partition of list_parted for values in (null, 'xy');
-- 
2.11.0

