diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index 5ee3775..426d9c7 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -138,7 +138,7 @@
 #include "utils/syscache.h"
 #include "utils/timestamp.h"
 #include "utils/typcache.h"
-
+#include "portability/instr_time.h" /* just for perf test debug */
 #define DEFAULT_PAGE_CPU_MULTIPLIER 50.0
 
 /*
@@ -3348,6 +3348,12 @@ mergejoinscansel(PlannerInfo *root, Node *clause,
 				rightmax;
 	double		selec;
 
+	/* just for perf test debug */
+	instr_time	comparestart,
+				compareuration;
+
+	INSTR_TIME_SET_CURRENT(comparestart);
+
 	/* Set default results if we can't figure anything out. */
 	/* XXX should default "start" fraction be a bit more than 0? */
 	*leftstart = *rightstart = 0.0;
@@ -3618,6 +3624,20 @@ mergejoinscansel(PlannerInfo *root, Node *clause,
 fail:
 	ReleaseVariableStats(leftvar);
 	ReleaseVariableStats(rightvar);
+
+	{							/* just for perf test debug */
+		double		plantime;
+
+		INSTR_TIME_SET_CURRENT(compareuration);
+		INSTR_TIME_SUBTRACT(compareuration, comparestart);
+		plantime = INSTR_TIME_GET_DOUBLE(compareuration);
+
+		elog(NOTICE, "mergejoinscansel() : %.*f"
+			 "\nv0 Selectivity: left:(%.*f, %.*f), right:(%.*f, %.*f)",
+			 3, 1000.0 * plantime,
+			 17, *leftstart, 17, *leftend,
+			 17, *rightstart, 17, *rightend);
+	}
 }