Prevent failures on partitioned distributed tables with statistics objects on PG 15

Comment from the code is clear on this:
/*
 * The statistics objects of the distributed table are not relevant
 * for the distributed planning, so we can override it.
 *
 * Normally, we should not need this. However, the combination of
 * Postgres commit 269b532aef55a579ae02a3e8e8df14101570dfd9 and
 * Citus function AdjustPartitioningForDistributedPlanning()
 * forces us to do this. The commit expects statistics objects
 * of partitions to have "inh" flag set properly. Whereas, the
 * function overrides "inh" flag. To avoid Postgres to throw error,
 * we override statlist such that Postgres does not try to process
 * any statistics objects during the standard_planner() on the
 * coordinator. In the end, we do not need the standard_planner()
 * on the coordinator to generate an optimized plan. We call
 * into standard_planner() for other purposes, such as generating the
 * relationRestrictionContext here.
 *
 * AdjustPartitioningForDistributedPlanning() is a hack that we use
 * to prevent Postgres' standard_planner() to expand all the partitions
 * for the distributed planning when a distributed partitioned table
 * is queried. It is required for both correctness and performance
 * reasons. Although we can eliminate the use of the function for
 * the correctness (e.g., make sure that rest of the planner can handle
 * partitions), it's performance implication is hard to avoid. Certain
 * planning logic of Citus (such as router or query pushdown) relies
 * heavily on the relationRestrictionList. If
 * AdjustPartitioningForDistributedPlanning() is removed, all the
 * partitions show up in the, causing high planning times for
 * such queries.
 */

src/backend/distributed/planner/distributed_planner.c

@@ -1897,14 +1897,14 @@ multi_relation_restriction_hook(PlannerInfo *root, RelOptInfo *relOptInfo,
 	MemoryContext restrictionsMemoryContext = plannerRestrictionContext->memoryContext;
 	MemoryContext oldMemoryContext = MemoryContextSwitchTo(restrictionsMemoryContext);
 
-	bool distributedTable = IsCitusTable(rte->relid);
+	bool isCitusTable = IsCitusTable(rte->relid);
 
 	RelationRestriction *relationRestriction = palloc0(sizeof(RelationRestriction));
 	relationRestriction->index = restrictionIndex;
 	relationRestriction->relationId = rte->relid;
 	relationRestriction->rte = rte;
 	relationRestriction->relOptInfo = relOptInfo;
-	relationRestriction->distributedRelation = distributedTable;
+	relationRestriction->citusTable = isCitusTable;
 	relationRestriction->plannerInfo = root;
 
 	/* see comments on GetVarFromAssignedParam() */
@@ -1919,10 +1919,42 @@ multi_relation_restriction_hook(PlannerInfo *root, RelOptInfo *relOptInfo,
 	 * We're also keeping track of whether all participant
 	 * tables are reference tables.
 	 */
-	if (distributedTable)
+	if (isCitusTable)
 	{
 		cacheEntry = GetCitusTableCacheEntry(rte->relid);
 
+		/*
+		 * The statistics objects of the distributed table are not relevant
+		 * for the distributed planning, so we can override it.
+		 *
+		 * Normally, we should not need this. However, the combination of
+		 * Postgres commit 269b532aef55a579ae02a3e8e8df14101570dfd9 and
+		 * Citus function AdjustPartitioningForDistributedPlanning()
+		 * forces us to do this. The commit expects statistics objects
+		 * of partitions to have "inh" flag set properly. Whereas, the
+		 * function overrides "inh" flag. To avoid Postgres to throw error,
+		 * we override statlist such that Postgres does not try to process
+		 * any statistics objects during the standard_planner() on the
+		 * coordinator. In the end, we do not need the standard_planner()
+		 * on the coordinator to generate an optimized plan. We call
+		 * into standard_planner() for other purposes, such as generating the
+		 * relationRestrictionContext here.
+		 *
+		 * AdjustPartitioningForDistributedPlanning() is a hack that we use
+		 * to prevent Postgres' standard_planner() to expand all the partitions
+		 * for the distributed planning when a distributed partitioned table
+		 * is queried. It is required for both correctness and performance
+		 * reasons. Although we can eliminate the use of the function for
+		 * the correctness (e.g., make sure that rest of the planner can handle
+		 * partitions), it's performance implication is hard to avoid. Certain
+		 * planning logic of Citus (such as router or query pushdown) relies
+		 * heavily on the relationRestrictionList. If
+		 * AdjustPartitioningForDistributedPlanning() is removed, all the
+		 * partitions show up in the, causing high planning times for
+		 * such queries.
+		 */
+		relOptInfo->statlist = NIL;
+
 		relationRestrictionContext->allReferenceTables &=
 			IsCitusTableTypeCacheEntry(cacheEntry, REFERENCE_TABLE);
 	}

src/backend/distributed/planner/multi_router_planner.c

@@ -3692,7 +3692,7 @@ CopyRelationRestrictionContext(RelationRestrictionContext *oldContext)
 
 		newRestriction->index = oldRestriction->index;
 		newRestriction->relationId = oldRestriction->relationId;
-		newRestriction->distributedRelation = oldRestriction->distributedRelation;
+		newRestriction->citusTable = oldRestriction->citusTable;
 		newRestriction->rte = copyObject(oldRestriction->rte);
 
 		/* can't be copied, we copy (flatly) a RelOptInfo, and then decouple baserestrictinfo */

src/backend/distributed/planner/relation_restriction_equivalence.c

@@ -224,7 +224,7 @@ ContextContainsLocalRelation(RelationRestrictionContext *restrictionContext)
 	{
 		RelationRestriction *relationRestriction = lfirst(relationRestrictionCell);
 
-		if (!relationRestriction->distributedRelation)
+		if (!relationRestriction->citusTable)
 		{
 			return true;
 		}

src/include/distributed/distributed_planner.h

@@ -56,7 +56,7 @@ typedef struct RelationRestriction
 {
 	Index index;
 	Oid relationId;
-	bool distributedRelation;
+	bool citusTable;
 	RangeTblEntry *rte;
 	RelOptInfo *relOptInfo;
 	PlannerInfo *plannerInfo;

src/test/regress/expected/multi_fix_partition_shard_index_names.out

@@ -521,9 +521,9 @@ SELECT tablename, indexname FROM pg_indexes WHERE schemaname = 'fix_idx_names' O
                  tablename                 |                        indexname
 ---------------------------------------------------------------------
  date_partitioned_citus_local_table        | date_partitioned_citus_local_table_measureid_idx
- date_partitioned_citus_local_table_361369 | date_partitioned_citus_local_table_measureid_idx_361369
+ date_partitioned_citus_local_table_361377 | date_partitioned_citus_local_table_measureid_idx_361377
  partition_local_table                     | partition_local_table_measureid_idx
- partition_local_table_361370              | partition_local_table_measureid_idx_361370
+ partition_local_table_361378              | partition_local_table_measureid_idx_361378
 (4 rows)
 
 -- creating a single object should only need to trigger fixing the single object
@@ -753,7 +753,7 @@ DETAIL:  drop cascades to table not_partitioned
 drop cascades to table not_distributed
 drop cascades to table fk_table
 drop cascades to table p
-drop cascades to table date_partitioned_citus_local_table_361369
+drop cascades to table date_partitioned_citus_local_table_361377
 drop cascades to table date_partitioned_citus_local_table
 drop cascades to table parent_table
 SELECT citus_remove_node('localhost', :master_port);

src/test/regress/expected/multi_partitioning.out

@@ -4324,12 +4324,66 @@ WHERE schemaname = 'partitioning_schema' AND tablename ilike '%part_table_with_%
 (6 rows)
 
 \c - - - :master_port
+SET search_path TO partitioning_schema;
+-- create parent table
+CREATE TABLE stxdinp(i int, a int, b int) PARTITION BY RANGE (i);
+-- create partition
+CREATE TABLE stxdinp1 PARTITION OF stxdinp FOR VALUES FROM (1) TO (100);
+-- populate table
+INSERT INTO stxdinp SELECT 1, a/100, a/100 FROM generate_series(1, 999) a;
+-- create extended statistics
+CREATE STATISTICS stxdinp ON a, b FROM stxdinp;
+-- distribute parent table
+SELECT create_distributed_table('stxdinp', 'i');
+NOTICE:  Copying data from local table...
+NOTICE:  copying the data has completed
+DETAIL:  The local data in the table is no longer visible, but is still on disk.
+HINT:  To remove the local data, run: SELECT truncate_local_data_after_distributing_table($$partitioning_schema.stxdinp1$$)
+ create_distributed_table
+---------------------------------------------------------------------
+
+(1 row)
+
+-- run select query, works fine
+SELECT a, b FROM stxdinp GROUP BY 1, 2;
+ a | b
+---------------------------------------------------------------------
+ 1 | 1
+ 3 | 3
+ 7 | 7
+ 2 | 2
+ 8 | 8
+ 0 | 0
+ 5 | 5
+ 6 | 6
+ 9 | 9
+ 4 | 4
+(10 rows)
+
+-- partitions are processed recursively for PG15+
+VACUUM ANALYZE stxdinp;
+SELECT a, b FROM stxdinp GROUP BY 1, 2;
+ a | b
+---------------------------------------------------------------------
+ 1 | 1
+ 3 | 3
+ 7 | 7
+ 2 | 2
+ 8 | 8
+ 0 | 0
+ 5 | 5
+ 6 | 6
+ 9 | 9
+ 4 | 4
+(10 rows)
+
 DROP SCHEMA partitioning_schema CASCADE;
-NOTICE:  drop cascades to 4 other objects
+NOTICE:  drop cascades to 5 other objects
-DETAIL:  drop cascades to table partitioning_schema."schema-test"
+DETAIL:  drop cascades to table "schema-test"
-drop cascades to table partitioning_schema.another_distributed_table
+drop cascades to table another_distributed_table
-drop cascades to table partitioning_schema.distributed_parent_table
+drop cascades to table distributed_parent_table
-drop cascades to table partitioning_schema.part_table_with_very_long_name
+drop cascades to table part_table_with_very_long_name
+drop cascades to table stxdinp
 RESET search_path;
 DROP TABLE IF EXISTS
 	partitioning_hash_test,

src/test/regress/sql/multi_partitioning.sql

@@ -2002,6 +2002,30 @@ SELECT tablename, indexname FROM pg_indexes
 WHERE schemaname = 'partitioning_schema' AND tablename ilike '%part_table_with_%' ORDER BY 1, 2;
 
 \c - - - :master_port
+SET search_path TO partitioning_schema;
+
+-- create parent table
+CREATE TABLE stxdinp(i int, a int, b int) PARTITION BY RANGE (i);
+
+-- create partition
+CREATE TABLE stxdinp1 PARTITION OF stxdinp FOR VALUES FROM (1) TO (100);
+
+-- populate table
+INSERT INTO stxdinp SELECT 1, a/100, a/100 FROM generate_series(1, 999) a;
+
+-- create extended statistics
+CREATE STATISTICS stxdinp ON a, b FROM stxdinp;
+
+-- distribute parent table
+SELECT create_distributed_table('stxdinp', 'i');
+
+-- run select query, works fine
+SELECT a, b FROM stxdinp GROUP BY 1, 2;
+
+-- partitions are processed recursively for PG15+
+VACUUM ANALYZE stxdinp;
+SELECT a, b FROM stxdinp GROUP BY 1, 2;
+
 DROP SCHEMA partitioning_schema CASCADE;
 RESET search_path;
 DROP TABLE IF EXISTS