diff --git a/src/backend/catalog/pg_aggregate.c b/src/backend/catalog/pg_aggregate.c
index 246776093e..be634b87e7 100644
--- a/src/backend/catalog/pg_aggregate.c
+++ b/src/backend/catalog/pg_aggregate.c
@@ -625,6 +625,7 @@ AggregateCreate(const char *aggName,
 							 PROVOLATILE_IMMUTABLE, /* volatility (not needed
 													 * for agg) */
 							 proparallel,
+							 false,				/* isPrivate, now false */
 							 parameterTypes,	/* paramTypes */
 							 allParameterTypes, /* allParamTypes */
 							 parameterModes,	/* parameterModes */
@@ -798,6 +799,8 @@ lookup_agg_function(List *fnName,
 	FuncDetailCode fdresult;
 	AclResult	aclresult;
 	int			i;
+	bool		is_private;
+	Oid			nspid;
 
 	/*
 	 * func_get_detail looks up the function in the catalogs, does
@@ -810,7 +813,8 @@ lookup_agg_function(List *fnName,
 							   nargs, input_types, false, false,
 							   &fnOid, rettype, &retset,
 							   &nvargs, &vatype,
-							   &true_oid_array, NULL);
+							   &true_oid_array, NULL,
+							   &is_private, &nspid);
 
 	/* only valid case is a normal function not returning a set */
 	if (fdresult != FUNCDETAIL_NORMAL || !OidIsValid(fnOid))
diff --git a/src/backend/catalog/pg_proc.c b/src/backend/catalog/pg_proc.c
index 9b4015d0d4..4b11485442 100644
--- a/src/backend/catalog/pg_proc.c
+++ b/src/backend/catalog/pg_proc.c
@@ -79,6 +79,7 @@ ProcedureCreate(const char *procedureName,
 				bool isStrict,
 				char volatility,
 				char parallel,
+				bool isPrivate,
 				oidvector *parameterTypes,
 				Datum allParameterTypes,
 				Datum parameterModes,
@@ -329,6 +330,7 @@ ProcedureCreate(const char *procedureName,
 	values[Anum_pg_proc_pronargdefaults - 1] = UInt16GetDatum(list_length(parameterDefaults));
 	values[Anum_pg_proc_prorettype - 1] = ObjectIdGetDatum(returnType);
 	values[Anum_pg_proc_proargtypes - 1] = PointerGetDatum(parameterTypes);
+	values[Anum_pg_proc_proisprivate - 1] = BoolGetDatum(isPrivate);
 	if (allParameterTypes != PointerGetDatum(NULL))
 		values[Anum_pg_proc_proallargtypes - 1] = allParameterTypes;
 	else
diff --git a/src/backend/commands/functioncmds.c b/src/backend/commands/functioncmds.c
index 68109bfda0..51907dd678 100644
--- a/src/backend/commands/functioncmds.c
+++ b/src/backend/commands/functioncmds.c
@@ -479,7 +479,8 @@ compute_common_attribute(ParseState *pstate,
 						 List **set_items,
 						 DefElem **cost_item,
 						 DefElem **rows_item,
-						 DefElem **parallel_item)
+						 DefElem **parallel_item,
+						 DefElem **scope_item)
 {
 	if (strcmp(defel->defname, "volatility") == 0)
 	{
@@ -546,6 +547,13 @@ compute_common_attribute(ParseState *pstate,
 
 		*parallel_item = defel;
 	}
+	else if (strcmp(defel->defname, "scope") == 0)
+	{
+		if (*scope_item)
+			goto duplicate_error;
+
+		*scope_item = defel;
+	}
 	else
 		return false;
 
@@ -655,7 +663,8 @@ compute_function_attributes(ParseState *pstate,
 							ArrayType **proconfig,
 							float4 *procost,
 							float4 *prorows,
-							char *parallel_p)
+							char *parallel_p,
+							bool *isPrivate)
 {
 	ListCell   *option;
 	DefElem    *as_item = NULL;
@@ -670,6 +679,7 @@ compute_function_attributes(ParseState *pstate,
 	DefElem    *cost_item = NULL;
 	DefElem    *rows_item = NULL;
 	DefElem    *parallel_item = NULL;
+	DefElem    *scope_item = NULL;
 
 	foreach(option, options)
 	{
@@ -726,7 +736,8 @@ compute_function_attributes(ParseState *pstate,
 										  &set_items,
 										  &cost_item,
 										  &rows_item,
-										  &parallel_item))
+										  &parallel_item,
+										  &scope_item))
 		{
 			/* recognized common option */
 			continue;
@@ -790,6 +801,11 @@ compute_function_attributes(ParseState *pstate,
 	}
 	if (parallel_item)
 		*parallel_p = interpret_func_parallel(parallel_item);
+	if (scope_item)
+	{
+		if (strcmp(strVal(scope_item->arg), "private") == 0)
+			*isPrivate = true;
+	}
 }
 
 
@@ -889,6 +905,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 				isStrict,
 				security,
 				isLeakProof;
+	bool		isPrivate;
 	char		volatility;
 	ArrayType  *proconfig;
 	float4		procost;
@@ -918,6 +935,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 	procost = -1;				/* indicates not set */
 	prorows = -1;				/* indicates not set */
 	parallel = PROPARALLEL_UNSAFE;
+	isPrivate = false;
 
 	/* Extract non-default attributes from stmt->options list */
 	compute_function_attributes(pstate,
@@ -926,7 +944,8 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 								&as_clause, &language, &transformDefElem,
 								&isWindowFunc, &volatility,
 								&isStrict, &security, &isLeakProof,
-								&proconfig, &procost, &prorows, &parallel);
+								&proconfig, &procost, &prorows, &parallel,
+								&isPrivate);
 
 	/* Look up the language and validate permissions */
 	languageTuple = SearchSysCache1(LANGNAME, PointerGetDatum(language));
@@ -1106,6 +1125,7 @@ CreateFunction(ParseState *pstate, CreateFunctionStmt *stmt)
 						   isStrict,
 						   volatility,
 						   parallel,
+						   isPrivate,
 						   parameterTypes,
 						   PointerGetDatum(allParameterTypes),
 						   PointerGetDatum(parameterModes),
@@ -1188,6 +1208,7 @@ AlterFunction(ParseState *pstate, AlterFunctionStmt *stmt)
 	DefElem    *cost_item = NULL;
 	DefElem    *rows_item = NULL;
 	DefElem    *parallel_item = NULL;
+	DefElem    *scope_item = NULL;
 	ObjectAddress address;
 
 	rel = heap_open(ProcedureRelationId, RowExclusiveLock);
@@ -1228,7 +1249,8 @@ AlterFunction(ParseState *pstate, AlterFunctionStmt *stmt)
 									 &set_items,
 									 &cost_item,
 									 &rows_item,
-									 &parallel_item) == false)
+									 &parallel_item,
+									 &scope_item) == false)
 			elog(ERROR, "option \"%s\" not recognized", defel->defname);
 	}
 
diff --git a/src/backend/commands/proclang.c b/src/backend/commands/proclang.c
index c900ad9431..35dd0a619a 100644
--- a/src/backend/commands/proclang.c
+++ b/src/backend/commands/proclang.c
@@ -134,6 +134,7 @@ CreateProceduralLanguage(CreatePLangStmt *stmt)
 									  false,	/* isStrict */
 									  PROVOLATILE_VOLATILE,
 									  PROPARALLEL_UNSAFE,
+									  false,	/* isPrivate */
 									  buildoidvector(funcargtypes, 0),
 									  PointerGetDatum(NULL),
 									  PointerGetDatum(NULL),
@@ -173,6 +174,7 @@ CreateProceduralLanguage(CreatePLangStmt *stmt)
 										  true, /* isStrict */
 										  PROVOLATILE_VOLATILE,
 										  PROPARALLEL_UNSAFE,
+										  false,	/* isPrivate */
 										  buildoidvector(funcargtypes, 1),
 										  PointerGetDatum(NULL),
 										  PointerGetDatum(NULL),
@@ -215,6 +217,7 @@ CreateProceduralLanguage(CreatePLangStmt *stmt)
 										  true, /* isStrict */
 										  PROVOLATILE_VOLATILE,
 										  PROPARALLEL_UNSAFE,
+										  false,	/* isPrivate */
 										  buildoidvector(funcargtypes, 1),
 										  PointerGetDatum(NULL),
 										  PointerGetDatum(NULL),
diff --git a/src/backend/commands/typecmds.c b/src/backend/commands/typecmds.c
index 175ecc8b48..9525b766a1 100644
--- a/src/backend/commands/typecmds.c
+++ b/src/backend/commands/typecmds.c
@@ -1675,6 +1675,7 @@ makeRangeConstructors(const char *name, Oid namespace,
 								 false, /* isStrict */
 								 PROVOLATILE_IMMUTABLE, /* volatility */
 								 PROPARALLEL_SAFE,	/* parallel safety */
+								 false, /* isPrivate */
 								 constructorArgTypesVector, /* parameterTypes */
 								 PointerGetDatum(NULL), /* allParameterTypes */
 								 PointerGetDatum(NULL), /* parameterModes */
diff --git a/src/backend/executor/execExpr.c b/src/backend/executor/execExpr.c
index e284fd71d7..54ba40d2d0 100644
--- a/src/backend/executor/execExpr.c
+++ b/src/backend/executor/execExpr.c
@@ -153,7 +153,7 @@ ExecInitExpr(Expr *node, PlanState *parent)
  * and instead we may have a ParamListInfo describing PARAM_EXTERN Params.
  */
 ExprState *
-ExecInitExprWithParams(Expr *node, ParamListInfo ext_params)
+ExecInitExprWithParams(Expr *node, ParamListInfo ext_params, Oid query_owner_nspid)
 {
 	ExprState  *state;
 	ExprEvalStep scratch = {0};
@@ -167,6 +167,7 @@ ExecInitExprWithParams(Expr *node, ParamListInfo ext_params)
 	state->expr = node;
 	state->parent = NULL;
 	state->ext_params = ext_params;
+	state->query_owner_nspid = query_owner_nspid;
 
 	/* Insert EEOP_*_FETCHSOME steps as needed */
 	ExecInitExprSlots(state, (Node *) node);
@@ -879,6 +880,25 @@ ExecInitExprRec(Expr *node, ExprState *state,
 			{
 				FuncExpr   *func = (FuncExpr *) node;
 
+				/* check scope of function */
+				if (func->funcprivate)
+				{
+					Oid		query_owner_nspid = state->query_owner_nspid;
+
+					if (OidIsValid(state->query_owner_nspid))
+						query_owner_nspid = state->query_owner_nspid;
+					else if (state->parent && state->parent->state)
+						query_owner_nspid =
+							  state->parent->state->es_query_owner_nspid;
+
+					if (!OidIsValid(query_owner_nspid))
+						elog(ERROR, "private function can be called only from routine");
+					if (query_owner_nspid != func->funcnspid)
+						elog(ERROR, "private function of \"%s\" used from function from \"%s\"",
+							 get_namespace_name(func->funcnspid),
+							 get_namespace_name(query_owner_nspid));
+				}
+
 				ExecInitFunc(&scratch, node,
 							 func->args, func->funcid, func->inputcollid,
 							 state);
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index c583e020a0..00ca74a804 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -824,6 +824,9 @@ InitPlan(QueryDesc *queryDesc, int eflags)
 	estate->es_range_table = rangeTable;
 	estate->es_plannedstmt = plannedstmt;
 
+	/* ToDo: Better to store query_owner_nspid to QueryDesc */
+	estate->es_query_owner_nspid = plannedstmt->query_owner_nspid;
+
 	/*
 	 * initialize result relation stuff, and open/lock the result rels.
 	 *
diff --git a/src/backend/executor/execParallel.c b/src/backend/executor/execParallel.c
index ee0f07a81e..ec88d8160e 100644
--- a/src/backend/executor/execParallel.c
+++ b/src/backend/executor/execParallel.c
@@ -1102,6 +1102,7 @@ ExecParallelGetQueryDesc(shm_toc *toc, DestReceiver *receiver,
 	PlannedStmt *pstmt;
 	ParamListInfo paramLI;
 	char	   *queryString;
+	Oid			query_owner_nspid;
 
 	/* Get the query string from shared memory */
 	queryString = shm_toc_lookup(toc, PARALLEL_KEY_QUERY_TEXT, false);
diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index 5b3eaec80b..8b7d52bf57 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -159,6 +159,8 @@ CreateExecutorState(void)
 
 	estate->es_use_parallel_mode = false;
 
+	estate->es_query_owner_nspid = InvalidOid;
+
 	estate->es_jit_flags = 0;
 	estate->es_jit = NULL;
 
diff --git a/src/backend/executor/spi.c b/src/backend/executor/spi.c
index 5756365c8f..6c01be90b9 100644
--- a/src/backend/executor/spi.c
+++ b/src/backend/executor/spi.c
@@ -2149,6 +2149,9 @@ _SPI_execute_plan(SPIPlanPtr plan, ParamListInfo paramLI,
 			_SPI_current->lastoid = InvalidOid;
 			_SPI_current->tuptable = NULL;
 
+			/* inject assigned query_owner_nspid */
+			stmt->query_owner_nspid = plan->query_owner_nspid;
+
 			if (stmt->utilityStmt)
 			{
 				if (IsA(stmt->utilityStmt, CopyStmt))
@@ -2200,6 +2203,11 @@ _SPI_execute_plan(SPIPlanPtr plan, ParamListInfo paramLI,
 				else
 					snap = InvalidSnapshot;
 
+				/*
+				 * ToDo: better place to inject query owner nspid, but
+				 * we should to implement passing query owner nspid over
+				 * parallel workers.
+				 */
 				qdesc = CreateQueryDesc(stmt,
 										plansource->query_string,
 										snap, crosscheck_snapshot,
@@ -2697,6 +2705,8 @@ _SPI_make_plan_non_temp(SPIPlanPtr plan)
 	/* For safety, unlink the CachedPlanSources from the temporary plan */
 	plan->plancache_list = NIL;
 
+	newplan->query_owner_nspid = plan->query_owner_nspid;
+
 	return newplan;
 }
 
@@ -2767,9 +2777,21 @@ _SPI_save_plan(SPIPlanPtr plan)
 		SaveCachedPlan(plansource);
 	}
 
+	newplan->query_owner_nspid = plan->query_owner_nspid;
+
 	return newplan;
 }
 
+/*
+ * Assign query owner namespace to plan. The query owner nspid
+ * is used for implementation of schema private functions.
+ */
+void
+assign_query_owner_nspid(SPIPlanPtr plan, Oid query_owner_nspid)
+{
+	plan->query_owner_nspid = query_owner_nspid;
+}
+
 /*
  * Internal lookup of ephemeral named relation by name.
  */
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 7c8220cf65..b52f287c35 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -102,6 +102,7 @@ _copyPlannedStmt(const PlannedStmt *from)
 	COPY_NODE_FIELD(utilityStmt);
 	COPY_LOCATION_FIELD(stmt_location);
 	COPY_LOCATION_FIELD(stmt_len);
+	COPY_SCALAR_FIELD(query_owner_nspid);
 
 	return newnode;
 }
@@ -1524,6 +1525,8 @@ _copyFuncExpr(const FuncExpr *from)
 	COPY_SCALAR_FIELD(funccollid);
 	COPY_SCALAR_FIELD(inputcollid);
 	COPY_NODE_FIELD(args);
+	COPY_SCALAR_FIELD(funcprivate);
+	COPY_SCALAR_FIELD(funcnspid);
 	COPY_LOCATION_FIELD(location);
 
 	return newnode;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 378f2facb8..144034760f 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -289,6 +289,8 @@ _equalFuncExpr(const FuncExpr *a, const FuncExpr *b)
 	COMPARE_SCALAR_FIELD(funccollid);
 	COMPARE_SCALAR_FIELD(inputcollid);
 	COMPARE_NODE_FIELD(args);
+	COMPARE_SCALAR_FIELD(funcprivate);
+	COMPARE_SCALAR_FIELD(funcnspid);
 	COMPARE_LOCATION_FIELD(location);
 
 	return true;
diff --git a/src/backend/nodes/makefuncs.c b/src/backend/nodes/makefuncs.c
index 1bd2599c2c..2e78dd8f18 100644
--- a/src/backend/nodes/makefuncs.c
+++ b/src/backend/nodes/makefuncs.c
@@ -526,6 +526,8 @@ makeFuncExpr(Oid funcid, Oid rettype, List *args,
 	funcexpr->funcresulttype = rettype;
 	funcexpr->funcretset = false;	/* only allowed case here */
 	funcexpr->funcvariadic = false; /* only allowed case here */
+	funcexpr->funcprivate = false;	/* only allowed case here */
+	funcexpr->funcnspid = InvalidOid;
 	funcexpr->funcformat = fformat;
 	funcexpr->funccollid = funccollid;
 	funcexpr->inputcollid = inputcollid;
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 6269f474d2..6a8cb3af23 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -287,6 +287,7 @@ _outPlannedStmt(StringInfo str, const PlannedStmt *node)
 	WRITE_NODE_FIELD(utilityStmt);
 	WRITE_LOCATION_FIELD(stmt_location);
 	WRITE_LOCATION_FIELD(stmt_len);
+	WRITE_OID_FIELD(query_owner_nspid);
 }
 
 /*
@@ -1278,6 +1279,8 @@ _outFuncExpr(StringInfo str, const FuncExpr *node)
 	WRITE_OID_FIELD(funccollid);
 	WRITE_OID_FIELD(inputcollid);
 	WRITE_NODE_FIELD(args);
+	WRITE_BOOL_FIELD(funcprivate);
+	WRITE_OID_FIELD(funcnspid);
 	WRITE_LOCATION_FIELD(location);
 }
 
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index 3254524223..7cde1caf47 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -680,6 +680,8 @@ _readFuncExpr(void)
 	READ_OID_FIELD(funccollid);
 	READ_OID_FIELD(inputcollid);
 	READ_NODE_FIELD(args);
+	READ_BOOL_FIELD(funcprivate);
+	READ_OID_FIELD(funcnspid);
 	READ_LOCATION_FIELD(location);
 
 	READ_DONE();
@@ -1494,6 +1496,7 @@ _readPlannedStmt(void)
 	READ_NODE_FIELD(utilityStmt);
 	READ_LOCATION_FIELD(stmt_location);
 	READ_LOCATION_FIELD(stmt_len);
+	READ_OID_FIELD(query_owner_nspid);
 
 	READ_DONE();
 }
diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index 01335db511..2ae754fdb5 100644
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -214,6 +214,7 @@ add_vars_to_targetlist(PlannerInfo *root, List *vars,
 
 			if (bms_is_subset(where_needed, rel->relids))
 				continue;
+
 			Assert(attno >= rel->min_attr && attno <= rel->max_attr);
 			attno -= rel->min_attr;
 			if (rel->attr_needed[attno] == NULL)
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 96bf0601a8..750d4ea430 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -532,6 +532,8 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	result->stmt_location = parse->stmt_location;
 	result->stmt_len = parse->stmt_len;
 
+	result->query_owner_nspid = InvalidOid;
+
 	result->jitFlags = PGJIT_NONE;
 	if (jit_enabled && jit_above_cost >= 0 &&
 		top_plan->total_cost > jit_above_cost)
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index a04ad6e99e..c9a6bd16b3 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -129,6 +129,7 @@ static Expr *simplify_function(Oid funcid,
 				  Oid result_type, int32 result_typmod,
 				  Oid result_collid, Oid input_collid, List **args_p,
 				  bool funcvariadic, bool process_args, bool allow_non_const,
+				  bool funcprivate, Oid funcnspid,
 				  eval_const_expressions_context *context);
 static List *reorder_function_arguments(List *args, HeapTuple func_tuple);
 static List *add_function_defaults(List *args, HeapTuple func_tuple);
@@ -138,11 +139,13 @@ static void recheck_cast_function_args(List *args, Oid result_type,
 static Expr *evaluate_function(Oid funcid, Oid result_type, int32 result_typmod,
 				  Oid result_collid, Oid input_collid, List *args,
 				  bool funcvariadic,
+				  bool funcprivate, Oid funcnspid,
 				  HeapTuple func_tuple,
 				  eval_const_expressions_context *context);
 static Expr *inline_function(Oid funcid, Oid result_type, Oid result_collid,
 				Oid input_collid, List *args,
 				bool funcvariadic,
+				bool funcprivate, Oid funcnspid,
 				HeapTuple func_tuple,
 				eval_const_expressions_context *context);
 static Node *substitute_actual_parameters(Node *expr, int nargs, List *args,
@@ -2686,6 +2689,8 @@ eval_const_expressions_mutator(Node *node,
 										   expr->funcvariadic,
 										   true,
 										   true,
+										   expr->funcprivate,
+										   expr->funcnspid,
 										   context);
 				if (simple)		/* successfully simplified it */
 					return (Node *) simple;
@@ -2705,6 +2710,8 @@ eval_const_expressions_mutator(Node *node,
 				newexpr->funccollid = expr->funccollid;
 				newexpr->inputcollid = expr->inputcollid;
 				newexpr->args = args;
+				newexpr->funcprivate = expr->funcprivate;
+				newexpr->funcnspid = expr->funcnspid;
 				newexpr->location = expr->location;
 				return (Node *) newexpr;
 			}
@@ -2733,6 +2740,8 @@ eval_const_expressions_mutator(Node *node,
 										   false,
 										   true,
 										   true,
+										   false,
+										   InvalidOid,
 										   context);
 				if (simple)		/* successfully simplified it */
 					return (Node *) simple;
@@ -2837,6 +2846,8 @@ eval_const_expressions_mutator(Node *node,
 											   false,
 											   false,
 											   false,
+											   false,
+											   InvalidOid,
 											   context);
 					if (simple) /* successfully simplified it */
 					{
@@ -3059,6 +3070,8 @@ eval_const_expressions_mutator(Node *node,
 										   false,
 										   true,
 										   true,
+										   false,
+										   InvalidOid,
 										   context);
 				if (simple)		/* successfully simplified output fn */
 				{
@@ -3091,6 +3104,8 @@ eval_const_expressions_mutator(Node *node,
 											   false,
 											   false,
 											   true,
+											   false,
+											   InvalidOid,
 											   context);
 					if (simple) /* successfully simplified input fn */
 						return (Node *) simple;
@@ -4023,6 +4038,7 @@ static Expr *
 simplify_function(Oid funcid, Oid result_type, int32 result_typmod,
 				  Oid result_collid, Oid input_collid, List **args_p,
 				  bool funcvariadic, bool process_args, bool allow_non_const,
+				  bool funcprivate, Oid funcnspid,
 				  eval_const_expressions_context *context)
 {
 	List	   *args = *args_p;
@@ -4068,6 +4084,7 @@ simplify_function(Oid funcid, Oid result_type, int32 result_typmod,
 	newexpr = evaluate_function(funcid, result_type, result_typmod,
 								result_collid, input_collid,
 								args, funcvariadic,
+								funcprivate, funcnspid,
 								func_tuple, context);
 
 	if (!newexpr && allow_non_const && OidIsValid(func_form->protransform))
@@ -4088,6 +4105,8 @@ simplify_function(Oid funcid, Oid result_type, int32 result_typmod,
 		fexpr.funccollid = result_collid;
 		fexpr.inputcollid = input_collid;
 		fexpr.args = args;
+		fexpr.funcprivate = funcprivate;
+		fexpr.funcnspid = funcnspid;
 		fexpr.location = -1;
 
 		newexpr = (Expr *)
@@ -4098,6 +4117,7 @@ simplify_function(Oid funcid, Oid result_type, int32 result_typmod,
 	if (!newexpr && allow_non_const)
 		newexpr = inline_function(funcid, result_type, result_collid,
 								  input_collid, args, funcvariadic,
+								  funcprivate, funcnspid,
 								  func_tuple, context);
 
 	ReleaseSysCache(func_tuple);
@@ -4337,6 +4357,7 @@ static Expr *
 evaluate_function(Oid funcid, Oid result_type, int32 result_typmod,
 				  Oid result_collid, Oid input_collid, List *args,
 				  bool funcvariadic,
+				  bool funcprivate, Oid funcnspid,
 				  HeapTuple func_tuple,
 				  eval_const_expressions_context *context)
 {
@@ -4423,6 +4444,8 @@ evaluate_function(Oid funcid, Oid result_type, int32 result_typmod,
 	newexpr->funccollid = result_collid;	/* doesn't matter */
 	newexpr->inputcollid = input_collid;
 	newexpr->args = args;
+	newexpr->funcprivate = funcprivate;
+	newexpr->funcnspid = funcnspid;
 	newexpr->location = -1;
 
 	return evaluate_expr((Expr *) newexpr, result_type, result_typmod,
@@ -4464,6 +4487,7 @@ static Expr *
 inline_function(Oid funcid, Oid result_type, Oid result_collid,
 				Oid input_collid, List *args,
 				bool funcvariadic,
+				bool funcprivate, Oid funcnspid,
 				HeapTuple func_tuple,
 				eval_const_expressions_context *context)
 {
@@ -4556,6 +4580,8 @@ inline_function(Oid funcid, Oid result_type, Oid result_collid,
 	fexpr->funccollid = result_collid;	/* doesn't matter */
 	fexpr->inputcollid = input_collid;
 	fexpr->args = args;
+	fexpr->funcprivate = funcprivate;
+	fexpr->funcnspid = funcnspid;
 	fexpr->location = -1;
 
 	pinfo = prepare_sql_fn_parse_info(func_tuple,
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 87f5e95827..13a87b33a4 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -664,7 +664,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 
 	PARALLEL PARSER PARTIAL PARTITION PASSING PASSWORD PLACING PLANS POLICY
 	POSITION PRECEDING PRECISION PRESERVE PREPARE PREPARED PRIMARY
-	PRIOR PRIVILEGES PROCEDURAL PROCEDURE PROCEDURES PROGRAM PUBLICATION
+	PRIOR PRIVATE PRIVILEGES PROCEDURAL PROCEDURE PROCEDURES PROGRAM PUBLICATION
 
 	QUOTE
 
@@ -7936,6 +7936,11 @@ common_func_opt_item:
 				{
 					$$ = makeDefElem("parallel", (Node *)makeString($2), @1);
 				}
+			| PRIVATE
+				{
+					/* This function can be called only from routines */
+					$$ = makeDefElem("scope", (Node *)makeString("private"), @1);
+				}
 		;
 
 createfunc_opt_item:
@@ -15181,6 +15186,7 @@ unreserved_keyword:
 			| PREPARED
 			| PRESERVE
 			| PRIOR
+			| PRIVATE
 			| PRIVILEGES
 			| PROCEDURAL
 			| PROCEDURE
diff --git a/src/backend/parser/parse_func.c b/src/backend/parser/parse_func.c
index 44257154b8..83aa22b053 100644
--- a/src/backend/parser/parse_func.c
+++ b/src/backend/parser/parse_func.c
@@ -102,6 +102,8 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 	bool		retset;
 	int			nvargs;
 	Oid			vatype;
+	bool		funcprivate;
+	Oid			funcnspid;
 	FuncDetailCode fdresult;
 	char		aggkind = 0;
 	ParseCallbackState pcbstate;
@@ -259,7 +261,8 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 							   !func_variadic, true,
 							   &funcid, &rettype, &retset,
 							   &nvargs, &vatype,
-							   &declared_arg_types, &argdefaults);
+							   &declared_arg_types, &argdefaults,
+							   &funcprivate, &funcnspid);
 
 	cancel_parser_errposition_callback(&pcbstate);
 
@@ -739,6 +742,8 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 		funcexpr->funcformat = COERCE_EXPLICIT_CALL;
 		/* funccollid and inputcollid will be set by parse_collate.c */
 		funcexpr->args = fargs;
+		funcexpr->funcprivate = funcprivate;
+		funcexpr->funcnspid = funcnspid;
 		funcexpr->location = location;
 
 		retval = (Node *) funcexpr;
@@ -1386,7 +1391,9 @@ func_get_detail(List *funcname,
 				int *nvargs,	/* return value */
 				Oid *vatype,	/* return value */
 				Oid **true_typeids, /* return value */
-				List **argdefaults) /* optional return value */
+				List **argdefaults, /* optional return value */
+				bool *isprivate,  /* return value */
+				Oid *namespace)	/* return value */
 {
 	FuncCandidateList raw_candidates;
 	FuncCandidateList best_candidate;
@@ -1610,6 +1617,10 @@ func_get_detail(List *funcname,
 		*rettype = pform->prorettype;
 		*retset = pform->proretset;
 		*vatype = pform->provariadic;
+
+		*isprivate = pform->proisprivate;
+		*namespace = pform->pronamespace;
+
 		/* fetch default args if caller wants 'em */
 		if (argdefaults && best_candidate->ndargs > 0)
 		{
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 03e9a28a63..f51693d7af 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -2588,6 +2588,9 @@ pg_get_functiondef(PG_FUNCTION_ARGS)
 	if (proc->proleakproof)
 		appendStringInfoString(&buf, " LEAKPROOF");
 
+	if (proc->proisprivate)
+		appendStringInfoString(&buf, " PRIVATE");
+
 	/* This code for the default cost and rows should match functioncmds.c */
 	if (proc->prolang == INTERNALlanguageId ||
 		proc->prolang == ClanguageId)
@@ -10765,6 +10768,8 @@ generate_function_name(Oid funcid, int nargs, List *argnames, Oid *argtypes,
 	Oid			p_vatype;
 	Oid		   *p_true_typeids;
 	bool		force_qualify = false;
+	bool		p_isprivate;
+	Oid			p_nspid;
 
 	proctup = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcid));
 	if (!HeapTupleIsValid(proctup))
@@ -10818,7 +10823,8 @@ generate_function_name(Oid funcid, int nargs, List *argnames, Oid *argtypes,
 								   !use_variadic, true,
 								   &p_funcid, &p_rettype,
 								   &p_retset, &p_nvargs, &p_vatype,
-								   &p_true_typeids, NULL);
+								   &p_true_typeids, NULL,
+								   &p_isprivate, &p_nspid);
 	else
 	{
 		p_result = FUNCDETAIL_NOTFOUND;
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 9baf7b2fde..63752d8fca 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -11532,6 +11532,7 @@ dumpFunc(Archive *fout, FuncInfo *finfo)
 	char	   *procost;
 	char	   *prorows;
 	char	   *proparallel;
+	char	   *proisprivate;
 	char	   *lanname;
 	char	   *rettypename;
 	int			nallargs;
@@ -11553,6 +11554,26 @@ dumpFunc(Archive *fout, FuncInfo *finfo)
 	asPart = createPQExpBuffer();
 
 	/* Fetch function-specific details */
+	if (fout->remoteVersion > 110000)
+	{
+		/*
+		 * proisprivate was added in 12
+		 */
+		appendPQExpBuffer(query,
+						  "SELECT proretset, prosrc, probin, "
+						  "pg_catalog.pg_get_function_arguments(oid) AS funcargs, "
+						  "pg_catalog.pg_get_function_identity_arguments(oid) AS funciargs, "
+						  "pg_catalog.pg_get_function_result(oid) AS funcresult, "
+						  "array_to_string(protrftypes, ' ') AS protrftypes, "
+						  "prokind, provolatile, proisstrict, prosecdef, "
+						  "proleakproof, proconfig, procost, prorows, "
+						  "proparallel, "
+						  "proisprivate, "
+						  "(SELECT lanname FROM pg_catalog.pg_language WHERE oid = prolang) AS lanname "
+						  "FROM pg_catalog.pg_proc "
+						  "WHERE oid = '%u'::pg_catalog.oid",
+						  finfo->dobj.catId.oid);
+	}
 	if (fout->remoteVersion >= 110000)
 	{
 		/*
@@ -11731,6 +11752,11 @@ dumpFunc(Archive *fout, FuncInfo *finfo)
 	else
 		proparallel = NULL;
 
+	if (PQfnumber(res, "proisprivate") != -1)
+		proisprivate = PQgetvalue(res, 0, PQfnumber(res, "proisprivate"));
+	else
+		proisprivate = NULL;
+
 	lanname = PQgetvalue(res, 0, PQfnumber(res, "lanname"));
 
 	/*
@@ -11914,6 +11940,8 @@ dumpFunc(Archive *fout, FuncInfo *finfo)
 	if (proleakproof[0] == 't')
 		appendPQExpBufferStr(q, " LEAKPROOF");
 
+
+
 	/*
 	 * COST and ROWS are emitted only if present and not default, so as not to
 	 * break backwards-compatibility of the dump without need.  Keep this code
@@ -11949,6 +11977,9 @@ dumpFunc(Archive *fout, FuncInfo *finfo)
 						  finfo->dobj.name);
 	}
 
+	if (proisprivate && proisprivate[0] == 't')
+		appendPQExpBuffer(q, " PRIVATE");
+
 	for (i = 0; i < nconfigitems; i++)
 	{
 		/* we feel free to scribble on configitems[] here */
diff --git a/src/include/catalog/pg_class.dat b/src/include/catalog/pg_class.dat
index 9fffdef379..48ab7b2ec8 100644
--- a/src/include/catalog/pg_class.dat
+++ b/src/include/catalog/pg_class.dat
@@ -47,7 +47,7 @@
   reloftype => '0', relowner => 'PGUID', relam => '0', relfilenode => '0',
   reltablespace => '0', relpages => '0', reltuples => '0', relallvisible => '0',
   reltoastrelid => '0', relhasindex => 'f', relisshared => 'f',
-  relpersistence => 'p', relkind => 'r', relnatts => '28', relchecks => '0',
+  relpersistence => 'p', relkind => 'r', relnatts => '29', relchecks => '0',
   relhasoids => 't', relhasrules => 'f', relhastriggers => 'f',
   relhassubclass => 'f', relrowsecurity => 'f', relforcerowsecurity => 'f',
   relispopulated => 't', relreplident => 'n', relispartition => 'f',
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index a34b2596fa..0b929a7365 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -75,6 +75,9 @@ CATALOG(pg_proc,1255,ProcedureRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(81,Proce
 	/* see PROPARALLEL_ categories below */
 	char		proparallel BKI_DEFAULT(s);
 
+	/* is it a private function? */
+	bool		proisprivate BKI_DEFAULT(f);
+
 	/* number of arguments */
 	/* Note: need not be given in pg_proc.dat; genbki.pl will compute it */
 	int16		pronargs;
@@ -192,6 +195,7 @@ extern ObjectAddress ProcedureCreate(const char *procedureName,
 				bool isStrict,
 				char volatility,
 				char parallel,
+				bool isPrivate,
 				oidvector *parameterTypes,
 				Datum allParameterTypes,
 				Datum parameterModes,
diff --git a/src/include/executor/execdesc.h b/src/include/executor/execdesc.h
index 10e9ded246..472ac5dce0 100644
--- a/src/include/executor/execdesc.h
+++ b/src/include/executor/execdesc.h
@@ -42,6 +42,7 @@ typedef struct QueryDesc
 	ParamListInfo params;		/* param values being passed in */
 	QueryEnvironment *queryEnv; /* query environment passed in */
 	int			instrument_options; /* OR of InstrumentOption flags */
+	Oid			query_owner_nspid; /* the query is evaluated from object assigned to schema */
 
 	/* These fields are set by ExecutorStart */
 	TupleDesc	tupDesc;		/* descriptor for result tuples */
diff --git a/src/include/executor/executor.h b/src/include/executor/executor.h
index f82b51667f..ce1f5349d7 100644
--- a/src/include/executor/executor.h
+++ b/src/include/executor/executor.h
@@ -242,7 +242,7 @@ ExecProcNode(PlanState *node)
  * prototypes from functions in execExpr.c
  */
 extern ExprState *ExecInitExpr(Expr *node, PlanState *parent);
-extern ExprState *ExecInitExprWithParams(Expr *node, ParamListInfo ext_params);
+extern ExprState *ExecInitExprWithParams(Expr *node, ParamListInfo ext_params, Oid query_owner_nspid);
 extern ExprState *ExecInitQual(List *qual, PlanState *parent);
 extern ExprState *ExecInitCheck(List *qual, PlanState *parent);
 extern List *ExecInitExprList(List *nodes, PlanState *parent);
diff --git a/src/include/executor/spi.h b/src/include/executor/spi.h
index 143a89a16c..df9037aa51 100644
--- a/src/include/executor/spi.h
+++ b/src/include/executor/spi.h
@@ -167,4 +167,6 @@ extern void SPICleanup(void);
 extern void AtEOXact_SPI(bool isCommit);
 extern void AtEOSubXact_SPI(bool isCommit, SubTransactionId mySubid);
 
+extern void assign_query_owner_nspid(SPIPlanPtr plan, Oid query_owner_nspid);
+
 #endif							/* SPI_H */
diff --git a/src/include/executor/spi_priv.h b/src/include/executor/spi_priv.h
index 401fd998f7..d6d88ab5a5 100644
--- a/src/include/executor/spi_priv.h
+++ b/src/include/executor/spi_priv.h
@@ -96,6 +96,7 @@ typedef struct _SPI_plan
 	Oid		   *argtypes;		/* Argument types (NULL if nargs is 0) */
 	ParserSetupHook parserSetup;	/* alternative parameter spec method */
 	void	   *parserSetupArg;
+	Oid			query_owner_nspid;
 } _SPI_plan;
 
 #endif							/* SPI_PRIV_H */
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 41fa2052a2..169bea82af 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -108,6 +108,8 @@ typedef struct ExprState
 
 	Datum	   *innermost_domainval;
 	bool	   *innermost_domainnull;
+
+	Oid			query_owner_nspid;
 } ExprState;
 
 
@@ -253,6 +255,9 @@ typedef struct ExprContext
 	/* Link to containing EState (NULL if a standalone ExprContext) */
 	struct EState *ecxt_estate;
 
+	/* Oid of namespace of object owning this query */
+	Oid			ecxt_query_owner_nspid;
+
 	/* Functions to call back when ExprContext is shut down or rescanned */
 	ExprContext_CB *ecxt_callbacks;
 } ExprContext;
@@ -564,6 +569,8 @@ typedef struct EState
 	/* The per-query shared memory area to use for parallel execution. */
 	struct dsa_area *es_query_dsa;
 
+	Oid			es_query_owner_nspid;
+
 	/*
 	 * JIT information. es_jit_flags indicates whether JIT should be performed
 	 * and with which options.  es_jit is created on-demand when JITing is
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 7c2abbd03a..94e29a857e 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -99,6 +99,8 @@ typedef struct PlannedStmt
 	/* statement location in source string (copied from Query) */
 	int			stmt_location;	/* start location, or -1 if unknown */
 	int			stmt_len;		/* length in bytes; 0 means "rest of string" */
+
+	Oid			query_owner_nspid;
 } PlannedStmt;
 
 /* macro for fetching the Plan associated with a SubPlan node */
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index 1b4b0d75af..0ddcd59e88 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -456,6 +456,8 @@ typedef struct FuncExpr
 	Oid			inputcollid;	/* OID of collation that function should use */
 	List	   *args;			/* arguments to the function */
 	int			location;		/* token location, or -1 if unknown */
+	bool		funcprivate;	/* true if function is private */
+	Oid			funcnspid;		/* OID of function namespace */
 } FuncExpr;
 
 /*
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 23db40147b..576f211adf 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -311,6 +311,7 @@ PG_KEYWORD("prepared", PREPARED, UNRESERVED_KEYWORD)
 PG_KEYWORD("preserve", PRESERVE, UNRESERVED_KEYWORD)
 PG_KEYWORD("primary", PRIMARY, RESERVED_KEYWORD)
 PG_KEYWORD("prior", PRIOR, UNRESERVED_KEYWORD)
+PG_KEYWORD("private", PRIVATE, UNRESERVED_KEYWORD)
 PG_KEYWORD("privileges", PRIVILEGES, UNRESERVED_KEYWORD)
 PG_KEYWORD("procedural", PROCEDURAL, UNRESERVED_KEYWORD)
 PG_KEYWORD("procedure", PROCEDURE, UNRESERVED_KEYWORD)
diff --git a/src/include/parser/parse_func.h b/src/include/parser/parse_func.h
index 11f9046e38..ae6cdc8f7a 100644
--- a/src/include/parser/parse_func.h
+++ b/src/include/parser/parse_func.h
@@ -41,7 +41,8 @@ extern FuncDetailCode func_get_detail(List *funcname,
 				bool expand_variadic, bool expand_defaults,
 				Oid *funcid, Oid *rettype,
 				bool *retset, int *nvargs, Oid *vatype,
-				Oid **true_typeids, List **argdefaults);
+				Oid **true_typeids, List **argdefaults,
+				bool *isprivate, Oid *namespace);
 
 extern int func_match_argtypes(int nargs,
 					Oid *input_typeids,
diff --git a/src/pl/plpgsql/src/pl_comp.c b/src/pl/plpgsql/src/pl_comp.c
index 721234d6d2..a35c61ec58 100644
--- a/src/pl/plpgsql/src/pl_comp.c
+++ b/src/pl/plpgsql/src/pl_comp.c
@@ -367,6 +367,7 @@ do_compile(FunctionCallInfo fcinfo,
 		function->fn_is_trigger = PLPGSQL_NOT_TRIGGER;
 
 	function->fn_prokind = procStruct->prokind;
+	function->fn_namespace = procStruct->pronamespace;
 
 	/*
 	 * Initialize the compiler, particularly the namespace stack.  The
diff --git a/src/pl/plpgsql/src/pl_exec.c b/src/pl/plpgsql/src/pl_exec.c
index 380d1de8f4..22efcbe80c 100644
--- a/src/pl/plpgsql/src/pl_exec.c
+++ b/src/pl/plpgsql/src/pl_exec.c
@@ -3989,6 +3989,9 @@ exec_prepare_plan(PLpgSQL_execstate *estate,
 	if (plan == NULL)
 		elog(ERROR, "SPI_prepare_params failed for \"%s\": %s",
 			 expr->query, SPI_result_code_string(SPI_result));
+
+	assign_query_owner_nspid(plan, estate->func->fn_namespace);
+
 	if (keepplan)
 		SPI_keepplan(plan);
 	expr->plan = plan;
@@ -6060,6 +6063,9 @@ exec_eval_simple_expr(PLpgSQL_execstate *estate,
 
 	econtext->ecxt_param_list_info = setup_param_list(estate, expr);
 
+	/* Setup query owner nspid - used for check of usage of private functions */
+	econtext->ecxt_query_owner_nspid = estate->func->fn_namespace;
+
 	/*
 	 * Prepare the expression for execution, if it's not been done already in
 	 * the current transaction.  (This will be forced to happen if we called
@@ -6070,7 +6076,8 @@ exec_eval_simple_expr(PLpgSQL_execstate *estate,
 		oldcontext = MemoryContextSwitchTo(estate->simple_eval_estate->es_query_cxt);
 		expr->expr_simple_state =
 			ExecInitExprWithParams(expr->expr_simple_expr,
-								   econtext->ecxt_param_list_info);
+								   econtext->ecxt_param_list_info,
+								   estate->func->fn_namespace);
 		expr->expr_simple_in_use = false;
 		expr->expr_simple_lxid = curlxid;
 		MemoryContextSwitchTo(oldcontext);
diff --git a/src/pl/plpgsql/src/plpgsql.h b/src/pl/plpgsql/src/plpgsql.h
index 4a4c7cbd36..a141a7e217 100644
--- a/src/pl/plpgsql/src/plpgsql.h
+++ b/src/pl/plpgsql/src/plpgsql.h
@@ -928,6 +928,7 @@ typedef struct PLpgSQL_function
 {
 	char	   *fn_signature;
 	Oid			fn_oid;
+	Oid			fn_namespace;
 	TransactionId fn_xmin;
 	ItemPointerData fn_tid;
 	PLpgSQL_trigtype fn_is_trigger;