diff --git a/contrib/pg_selectivities/.gitignore b/contrib/pg_selectivities/.gitignore
new file mode 100644
index 0000000..5dcb3ff
--- /dev/null
+++ b/contrib/pg_selectivities/.gitignore
@@ -0,0 +1,4 @@
+# Generated subdirectories
+/log/
+/results/
+/tmp_check/
diff --git a/contrib/pg_selectivities/Makefile b/contrib/pg_selectivities/Makefile
new file mode 100644
index 0000000..9843326
--- /dev/null
+++ b/contrib/pg_selectivities/Makefile
@@ -0,0 +1,21 @@
+# contrib/pg_selectivities/Makefile
+
+MODULE_big = pg_selectivities
+OBJS = pg_selectivities.o $(WIN32RES)
+
+EXTENSION = pg_selectivities
+DATA = pg_selectivities--1.0.sql
+PGFILEDESC = "pg_selectivities - functions to implemente planner hints"
+
+REGRESS = pg_selectivities
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = contrib/pg_selectivities
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif
diff --git a/contrib/pg_selectivities/expected/pg_selectivities.out b/contrib/pg_selectivities/expected/pg_selectivities.out
new file mode 100644
index 0000000..11fdf3f
--- /dev/null
+++ b/contrib/pg_selectivities/expected/pg_selectivities.out
@@ -0,0 +1,30 @@
+set cpu_operator_cost TO 0;
+set cpu_tuple_cost TO 0;
+create extension pg_selectivities;
+explain  select * from (select 7 from generate_series(1,1000000)) foo(x) where x=7;
+                                QUERY PLAN                                
+--------------------------------------------------------------------------
+ Function Scan on generate_series  (cost=0.00..0.00 rows=1000000 width=4)
+(1 row)
+
+explain  select * from (select 7 from generate_series(1,1000000)) foo(x) where x=7 and pg_always(1);
+                                QUERY PLAN                                
+--------------------------------------------------------------------------
+ Function Scan on generate_series  (cost=0.00..0.00 rows=1000000 width=4)
+   Filter: pg_always('1'::double precision)
+(2 rows)
+
+explain  select * from (select 7 from generate_series(1,1000000)) foo(x) where x=7 and pg_always(0.001);
+                              QUERY PLAN                               
+-----------------------------------------------------------------------
+ Function Scan on generate_series  (cost=0.00..0.00 rows=1000 width=4)
+   Filter: pg_always('0.001'::double precision)
+(2 rows)
+
+explain  select * from (select 7 from generate_series(1,1000000)) foo(x) where x=6 or pg_never(0.01);
+                               QUERY PLAN                               
+------------------------------------------------------------------------
+ Function Scan on generate_series  (cost=0.00..0.00 rows=10000 width=4)
+   Filter: pg_never('0.01'::double precision)
+(2 rows)
+
diff --git a/contrib/pg_selectivities/pg_selectivities--1.0.sql b/contrib/pg_selectivities/pg_selectivities--1.0.sql
new file mode 100644
index 0000000..90307a8
--- /dev/null
+++ b/contrib/pg_selectivities/pg_selectivities--1.0.sql
@@ -0,0 +1,21 @@
+/* contrib/pg_selectivities/pg_selectivities--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION pg_selectivities" to load this file. \quit
+
+CREATE FUNCTION pg_selectivities_support(internal)
+RETURNS internal
+AS 'MODULE_PATHNAME'
+LANGUAGE C IMMUTABLE STRICT PARALLEL SAFE;
+
+CREATE FUNCTION pg_always(float)
+RETURNS boolean
+AS 'MODULE_PATHNAME' 
+LANGUAGE C STRICT PARALLEL SAFE
+SUPPORT pg_selectivities_support;
+
+CREATE FUNCTION pg_never(float)
+RETURNS boolean
+AS 'MODULE_PATHNAME' 
+LANGUAGE C STRICT PARALLEL SAFE
+SUPPORT pg_selectivities_support;
diff --git a/contrib/pg_selectivities/pg_selectivities.c b/contrib/pg_selectivities/pg_selectivities.c
new file mode 100644
index 0000000..9a8ef54
--- /dev/null
+++ b/contrib/pg_selectivities/pg_selectivities.c
@@ -0,0 +1,50 @@
+/*
+ * contrib/pg_selectivities/pg_selectivities.c
+ */
+#include "postgres.h"
+#include "nodes/supportnodes.h"
+#include "fmgr.h"
+
+PG_MODULE_MAGIC;
+
+PG_FUNCTION_INFO_V1(pg_selectivities_support);
+PG_FUNCTION_INFO_V1(pg_always);
+PG_FUNCTION_INFO_V1(pg_never);
+
+Datum
+pg_selectivities_support(PG_FUNCTION_ARGS)
+{
+	Node	 *rawreq = (Node *) PG_GETARG_POINTER(0);
+	Node	 *ret = NULL;
+
+	if (IsA(rawreq, SupportRequestSelectivity))
+	{
+		SupportRequestSelectivity *req = (SupportRequestSelectivity *) rawreq;
+		if (list_length(req->args) == 1)
+		{
+			Node * node;
+			node=(Node*) linitial(req->args);
+			if (IsA(node, Const))
+			{
+				Selectivity s1;
+				s1= DatumGetFloat8(((Const*)node)->constvalue);
+				req->selectivity = s1;
+				ret = (Node *) req;
+			}
+		}
+	}
+
+	PG_RETURN_POINTER(ret);
+}
+
+Datum
+pg_always(PG_FUNCTION_ARGS)
+{
+	PG_RETURN_BOOL(true);
+}
+
+Datum
+pg_never(PG_FUNCTION_ARGS)
+{
+	PG_RETURN_BOOL(false);
+}
diff --git a/contrib/pg_selectivities/pg_selectivities.control b/contrib/pg_selectivities/pg_selectivities.control
new file mode 100644
index 0000000..1605068
--- /dev/null
+++ b/contrib/pg_selectivities/pg_selectivities.control
@@ -0,0 +1,5 @@
+# pg_selectivities extension
+comment = 'functions which always return true or false, but report a custom selectivity'
+default_version = '1.0'
+module_pathname = '$libdir/pg_selectivities'
+relocatable = true
diff --git a/contrib/pg_selectivities/sql/pg_selectivities.sql b/contrib/pg_selectivities/sql/pg_selectivities.sql
new file mode 100644
index 0000000..47dd0fc
--- /dev/null
+++ b/contrib/pg_selectivities/sql/pg_selectivities.sql
@@ -0,0 +1,8 @@
+set cpu_operator_cost TO 0;
+set cpu_tuple_cost TO 0;
+create extension pg_selectivities;
+
+explain  select * from (select 7 from generate_series(1,1000000)) foo(x) where x=7;
+explain  select * from (select 7 from generate_series(1,1000000)) foo(x) where x=7 and pg_always(1);
+explain  select * from (select 7 from generate_series(1,1000000)) foo(x) where x=7 and pg_always(0.001);
+explain  select * from (select 7 from generate_series(1,1000000)) foo(x) where x=6 or pg_never(0.01);