Preserve attstattarget on REINDEX CONCURRENTLY

diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 5a70fe4d2c..b4adb32af0 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -107,7 +107,8 @@ static TupleDesc ConstructTupleDescriptor(Relation heapRelation,
 										  List *indexColNames,
 										  Oid accessMethodObjectId,
 										  Oid *collationObjectId,
-										  Oid *classObjectId);
+										  Oid *classObjectId,
+										  int32 *attstattargets);
 static void InitializeAttributeOids(Relation indexRelation,
 									int numatts, Oid indexoid);
 static void AppendAttributeTuples(Relation indexRelation, Datum *attopts);
@@ -272,7 +273,8 @@ ConstructTupleDescriptor(Relation heapRelation,
 						 List *indexColNames,
 						 Oid accessMethodObjectId,
 						 Oid *collationObjectId,
-						 Oid *classObjectId)
+						 Oid *classObjectId,
+						 int32 *attstattargets)
 {
 	int			numatts = indexInfo->ii_NumIndexAttrs;
 	int			numkeyatts = indexInfo->ii_NumIndexKeyAttrs;
@@ -310,12 +312,14 @@ ConstructTupleDescriptor(Relation heapRelation,
 
 		MemSet(to, 0, ATTRIBUTE_FIXED_PART_SIZE);
 		to->attnum = i + 1;
-		to->attstattarget = -1;
 		to->attcacheoff = -1;
 		to->attislocal = true;
 		to->attcollation = (i < numkeyatts) ?
 			collationObjectId[i] : InvalidOid;
-
+		if(attstattargets != NULL)
+			to->attstattarget = attstattargets[i];
+		else
+			to->attstattarget = -1;
 		/*
 		 * Set the attribute name as specified by caller.
 		 */
@@ -697,6 +701,7 @@ index_create(Relation heapRelation,
 			 Oid *collationObjectId,
 			 Oid *classObjectId,
 			 int16 *coloptions,
+			 int32 *colstattargets,
 			 Datum reloptions,
 			 bits16 flags,
 			 bits16 constr_flags,
@@ -882,7 +887,8 @@ index_create(Relation heapRelation,
 											indexColNames,
 											accessMethodObjectId,
 											collationObjectId,
-											classObjectId);
+											classObjectId,
+											colstattargets);
 
 	/*
 	 * Allocate an OID for the index, unless we were told what to use.
@@ -1413,11 +1419,13 @@ index_concurrently_create_copy(Relation heapRelation, Oid oldIndexId,
 				optionDatum;
 	oidvector  *indclass;
 	int2vector *indcoloptions;
+	int32      *colstattargets;
 	bool		isnull;
 	List	   *indexColNames = NIL;
 	List	   *indexExprs = NIL;
 	List	   *indexPreds = NIL;
 
+
 	indexRelation = index_open(oldIndexId, RowExclusiveLock);
 
 	/* The new index needs some information from the old index */
@@ -1501,10 +1509,11 @@ index_concurrently_create_copy(Relation heapRelation, Oid oldIndexId,
 							true);
 
 	/*
-	 * Extract the list of column names and the column numbers for the new
+	 * Extract the list of column names, column numbers and stattargets for the new
 	 * index information.  All this information will be used for the index
 	 * creation.
 	 */
+	colstattargets = palloc(sizeof(int32) * oldInfo->ii_NumIndexAttrs);
 	for (int i = 0; i < oldInfo->ii_NumIndexAttrs; i++)
 	{
 		TupleDesc	indexTupDesc = RelationGetDescr(indexRelation);
@@ -1512,8 +1521,8 @@ index_concurrently_create_copy(Relation heapRelation, Oid oldIndexId,
 
 		indexColNames = lappend(indexColNames, NameStr(att->attname));
 		newInfo->ii_IndexAttrNumbers[i] = oldInfo->ii_IndexAttrNumbers[i];
+		colstattargets[i] = att->attstattarget;
 	}
-
 	/*
 	 * Now create the new index.
 	 *
@@ -1534,13 +1543,14 @@ index_concurrently_create_copy(Relation heapRelation, Oid oldIndexId,
 							  indexRelation->rd_indcollation,
 							  indclass->values,
 							  indcoloptions->values,
+							  colstattargets,
 							  optionDatum,
 							  INDEX_CREATE_SKIP_BUILD | INDEX_CREATE_CONCURRENT,
 							  0,
 							  true, /* allow table to be a system catalog? */
 							  false,	/* is_internal? */
 							  NULL);
-
+	pfree(colstattargets);
 	/* Close the relations used and clean up */
 	index_close(indexRelation, NoLock);
 	ReleaseSysCache(indexTuple);
diff --git a/src/backend/catalog/toasting.c b/src/backend/catalog/toasting.c
index d7b806020d..09c1be3611 100644
--- a/src/backend/catalog/toasting.c
+++ b/src/backend/catalog/toasting.c
@@ -313,7 +313,7 @@ create_toast_table(Relation rel, Oid toastOid, Oid toastIndexOid,
 				 list_make2("chunk_id", "chunk_seq"),
 				 BTREE_AM_OID,
 				 rel->rd_rel->reltablespace,
-				 collationObjectId, classObjectId, coloptions, (Datum) 0,
+				 collationObjectId, classObjectId, coloptions, NULL, (Datum) 0,
 				 INDEX_CREATE_IS_PRIMARY, 0, true, true, NULL);
 
 	table_close(toast_rel, NoLock);
diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
index 127ba7835d..6eba68c7ba 100644
--- a/src/backend/commands/indexcmds.c
+++ b/src/backend/commands/indexcmds.c
@@ -1140,7 +1140,7 @@ DefineIndex(Oid relationId,
 					 stmt->oldNode, indexInfo, indexColNames,
 					 accessMethodId, tablespaceId,
 					 collationObjectId, classObjectId,
-					 coloptions, reloptions,
+					 coloptions, NULL, reloptions,
 					 flags, constr_flags,
 					 allowSystemTableMods, !check_rights,
 					 &createdConstraintId);
diff --git a/src/include/catalog/index.h b/src/include/catalog/index.h
index e22d506436..bf9bc6bcef 100644
--- a/src/include/catalog/index.h
+++ b/src/include/catalog/index.h
@@ -79,6 +79,7 @@ extern Oid	index_create(Relation heapRelation,
 						 Oid *collationObjectId,
 						 Oid *classObjectId,
 						 int16 *coloptions,
+						 int32 *colstattargets,
 						 Datum reloptions,
 						 bits16 flags,
 						 bits16 constr_flags,
diff --git a/src/test/regress/expected/alter_table.out b/src/test/regress/expected/alter_table.out
index 0ce6ee4622..a9140bc837 100644
--- a/src/test/regress/expected/alter_table.out
+++ b/src/test/regress/expected/alter_table.out
@@ -113,6 +113,27 @@ ALTER INDEX attmp_idx ALTER COLUMN 2 SET STATISTICS 1000;
  b      | cstring          | yes  | b          | plain   | 
 btree, for table "public.attmp"
 
+-- Check we keep statistics after REINDEX and REINDEX CONCURRENTLY
+REINDEX INDEX attmp_idx;
+\d+ attmp_idx
+                        Index "public.attmp_idx"
+ Column |       Type       | Key? | Definition | Storage | Stats target 
+--------+------------------+------+------------+---------+--------------
+ a      | integer          | yes  | a          | plain   | 
+ expr   | double precision | yes  | (d + e)    | plain   | 1000
+ b      | cstring          | yes  | b          | plain   | 
+btree, for table "public.attmp"
+
+REINDEX INDEX CONCURRENTLY attmp_idx;
+\d+ attmp_idx
+                        Index "public.attmp_idx"
+ Column |       Type       | Key? | Definition | Storage | Stats target 
+--------+------------------+------+------------+---------+--------------
+ a      | integer          | yes  | a          | plain   | 
+ expr   | double precision | yes  | (d + e)    | plain   | 1000
+ b      | cstring          | yes  | b          | plain   | 
+btree, for table "public.attmp"
+
 ALTER INDEX attmp_idx ALTER COLUMN 3 SET STATISTICS 1000;
 ERROR:  cannot alter statistics on non-expression column "b" of index "attmp_idx"
 HINT:  Alter statistics on table column instead.
diff --git a/src/test/regress/sql/alter_table.sql b/src/test/regress/sql/alter_table.sql
index 4cc55d8525..36b24bfeb0 100644
--- a/src/test/regress/sql/alter_table.sql
+++ b/src/test/regress/sql/alter_table.sql
@@ -150,6 +150,15 @@ ALTER INDEX attmp_idx ALTER COLUMN 2 SET STATISTICS 1000;
 
 \d+ attmp_idx
 
+-- Check we keep statistics after REINDEX and REINDEX CONCURRENTLY
+REINDEX INDEX attmp_idx;
+
+\d+ attmp_idx
+
+REINDEX INDEX CONCURRENTLY attmp_idx;
+
+\d+ attmp_idx
+
 ALTER INDEX attmp_idx ALTER COLUMN 3 SET STATISTICS 1000;
 
 ALTER INDEX attmp_idx ALTER COLUMN 4 SET STATISTICS 1000;

diff --git a/src/include/utils/lsyscache.h b/src/include/utils/lsyscache.h
index ae720c1496..77871aaefc 100644
--- a/src/include/utils/lsyscache.h
+++ b/src/include/utils/lsyscache.h
@@ -90,6 +90,7 @@ extern Oid	get_opfamily_proc(Oid opfamily, Oid lefttype, Oid righttype,
 							  int16 procnum);
 extern char *get_attname(Oid relid, AttrNumber attnum, bool missing_ok);
 extern AttrNumber get_attnum(Oid relid, const char *attname);
+extern int	get_attstattarget(Oid relid, AttrNumber attnum);
 extern char get_attgenerated(Oid relid, AttrNumber attnum);
 extern Oid	get_atttype(Oid relid, AttrNumber attnum);
 extern void get_atttypetypmodcoll(Oid relid, AttrNumber attnum,
diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 1cb9172a5f..9403ae64f8 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -1884,6 +1884,63 @@ index_concurrently_swap(Oid newIndexId, Oid oldIndexId, const char *oldName)
 	/* Copy data of pg_statistic from the old index to the new one */
 	CopyStatistics(oldIndexId, newIndexId);
 
+	/* Copy pg_attribute.attstattarget for each index attribute */
+	{
+		HeapTuple	attrTuple;
+		Relation	pg_attribute;
+		SysScanDesc scan;
+		ScanKeyData key[1];
+
+		pg_attribute = table_open(AttributeRelationId, RowExclusiveLock);
+		ScanKeyInit(&key[0],
+					Anum_pg_attribute_attrelid,
+					BTEqualStrategyNumber, F_OIDEQ,
+					ObjectIdGetDatum(newIndexId));
+		scan = systable_beginscan(pg_attribute, AttributeRelidNumIndexId,
+								  true, NULL, 1, key);
+
+		while (HeapTupleIsValid((attrTuple = systable_getnext(scan))))
+		{
+			Form_pg_attribute att = (Form_pg_attribute) GETSTRUCT(attrTuple);
+			Datum		repl_val[Natts_pg_attribute];
+			bool		repl_null[Natts_pg_attribute];
+			bool		repl_repl[Natts_pg_attribute];
+			int			attstattarget;
+			HeapTuple	newTuple;
+
+			/* Ignore dropped columns */
+			if (att->attisdropped)
+				continue;
+
+			/*
+			 * Get attstattarget from the old index and refresh the new
+			 * value.
+			 */
+			attstattarget = get_attstattarget(oldIndexId, att->attnum);
+
+			/* no need for a refresh if both match */
+			if (attstattarget == att->attstattarget)
+				continue;
+
+			memset(repl_null, false, sizeof(repl_null));
+			memset(repl_repl, false, sizeof(repl_repl));
+
+			repl_repl[Anum_pg_attribute_attstattarget - 1] = true;
+			repl_val[Anum_pg_attribute_attstattarget - 1] = Int32GetDatum(attstattarget);
+
+			newTuple = heap_modify_tuple(attrTuple,
+										 RelationGetDescr(pg_attribute),
+										 repl_val, repl_null, repl_repl);
+			CatalogTupleUpdate(pg_attribute, &newTuple->t_self, newTuple);
+
+			heap_freetuple(newTuple);
+		}
+
+		systable_endscan(scan);
+		table_close(pg_attribute, RowExclusiveLock);
+	}
+
+
 	/* Close relations */
 	table_close(pg_class, RowExclusiveLock);
 	table_close(pg_index, RowExclusiveLock);
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 85c458bc46..6bba5f8ec4 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -871,6 +871,33 @@ get_attnum(Oid relid, const char *attname)
 		return InvalidAttrNumber;
 }
 
+/*
+ * get_attstattarget
+ *
+ *		Given the relation id and the attribute number,
+ *		return the "attstattarget" field from the attribute relation.
+ *
+ *		Errors if not found.
+ */
+int
+get_attstattarget(Oid relid, AttrNumber attnum)
+{
+	HeapTuple	tp;
+	Form_pg_attribute att_tup;
+	int			result;
+
+	tp = SearchSysCache2(ATTNUM,
+						 ObjectIdGetDatum(relid),
+						 Int16GetDatum(attnum));
+	if (!HeapTupleIsValid(tp))
+		elog(ERROR, "cache lookup failed for attribute %d of relation %u",
+			 attnum, relid);
+	att_tup = (Form_pg_attribute) GETSTRUCT(tp);
+	result = att_tup->attstattarget;
+	ReleaseSysCache(tp);
+	return result;
+}
+
 /*
  * get_attgenerated
  *
diff --git a/src/test/regress/expected/create_index.out b/src/test/regress/expected/create_index.out
index ce734f7ef3..2c07940b98 100644
--- a/src/test/regress/expected/create_index.out
+++ b/src/test/regress/expected/create_index.out
@@ -2559,6 +2559,7 @@ CREATE UNIQUE INDEX concur_exprs_index_pred ON concur_exprs_tab (c1)
 CREATE UNIQUE INDEX concur_exprs_index_pred_2
   ON concur_exprs_tab ((1 / c1))
   WHERE ('-H') >= (c2::TEXT) COLLATE "C";
+ALTER INDEX concur_exprs_index_expr ALTER COLUMN 1 SET STATISTICS 100;
 ANALYZE concur_exprs_tab;
 SELECT starelid::regclass, count(*) FROM pg_statistic WHERE starelid IN (
   'concur_exprs_index_expr'::regclass,
@@ -2638,6 +2639,20 @@ SELECT starelid::regclass, count(*) FROM pg_statistic WHERE starelid IN (
  concur_exprs_index_expr |     1
 (1 row)
 
+-- attstattarget should remain intact
+SELECT attrelid::regclass, attnum, attstattarget
+  FROM pg_attribute WHERE attrelid IN (
+    'concur_exprs_index_expr'::regclass,
+    'concur_exprs_index_pred'::regclass,
+    'concur_exprs_index_pred_2'::regclass)
+  ORDER BY 'concur_exprs_index_expr'::regclass::text, attnum;
+         attrelid          | attnum | attstattarget 
+---------------------------+--------+---------------
+ concur_exprs_index_expr   |      1 |           100
+ concur_exprs_index_pred   |      1 |            -1
+ concur_exprs_index_pred_2 |      1 |            -1
+(3 rows)
+
 DROP TABLE concur_exprs_tab;
 -- Temporary tables and on-commit actions, where CONCURRENTLY is ignored.
 -- ON COMMIT PRESERVE ROWS, the default.
diff --git a/src/test/regress/sql/create_index.sql b/src/test/regress/sql/create_index.sql
index fd4f30876e..0f00275274 100644
--- a/src/test/regress/sql/create_index.sql
+++ b/src/test/regress/sql/create_index.sql
@@ -1079,6 +1079,7 @@ CREATE UNIQUE INDEX concur_exprs_index_pred ON concur_exprs_tab (c1)
 CREATE UNIQUE INDEX concur_exprs_index_pred_2
   ON concur_exprs_tab ((1 / c1))
   WHERE ('-H') >= (c2::TEXT) COLLATE "C";
+ALTER INDEX concur_exprs_index_expr ALTER COLUMN 1 SET STATISTICS 100;
 ANALYZE concur_exprs_tab;
 SELECT starelid::regclass, count(*) FROM pg_statistic WHERE starelid IN (
   'concur_exprs_index_expr'::regclass,
@@ -1103,6 +1104,13 @@ SELECT starelid::regclass, count(*) FROM pg_statistic WHERE starelid IN (
   'concur_exprs_index_pred'::regclass,
   'concur_exprs_index_pred_2'::regclass)
   GROUP BY starelid ORDER BY starelid::regclass::text;
+-- attstattarget should remain intact
+SELECT attrelid::regclass, attnum, attstattarget
+  FROM pg_attribute WHERE attrelid IN (
+    'concur_exprs_index_expr'::regclass,
+    'concur_exprs_index_pred'::regclass,
+    'concur_exprs_index_pred_2'::regclass)
+  ORDER BY 'concur_exprs_index_expr'::regclass::text, attnum;
 DROP TABLE concur_exprs_tab;
 
 -- Temporary tables and on-commit actions, where CONCURRENTLY is ignored.