origpatch-simplified.patch

diff --git a/src/backend/access/gist/gistutil.c b/src/backend/access/gist/gistutil.c
index 8b60774..af4d4ea 100644
--- a/src/backend/access/gist/gistutil.c
+++ b/src/backend/access/gist/gistutil.c
@@ -375,6 +375,7 @@ gistchoose(Relation r, Page p, IndexTuple it,	/* it has compressed entry */
 	OffsetNumber result;
 	OffsetNumber maxoff;
 	OffsetNumber i;
+	OffsetNumber offsets[MaxOffsetNumber];
 	float		best_penalty[INDEX_MAX_KEYS];
 	GISTENTRY	entry,
 				identry[INDEX_MAX_KEYS];
@@ -407,11 +408,43 @@ gistchoose(Relation r, Page p, IndexTuple it,	/* it has compressed entry */
 	maxoff = PageGetMaxOffsetNumber(p);
 	Assert(maxoff >= FirstOffsetNumber);
 
-	for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
+	if (true)
 	{
-		IndexTuple	itup = (IndexTuple) PageGetItem(p, PageGetItemId(p, i));
-		bool		zero_penalty;
-		int			j;
+		/*
+		 * If randomization is required then prepare array of offset numbers
+		 * in order to remember which offset numbers were already exanimed.
+		 */
+		for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
+			offsets[i - FirstOffsetNumber] = i;
+	}
+
+	for (i = 0; i < maxoff; i++)
+	{
+		IndexTuple		itup;
+		bool			zero_penalty;
+		int				j;
+		OffsetNumber	offset;
+
+		if (true)
+		{
+			/*
+			 * Randomization: select random offset number from those which
+			 * aren't previously selected.
+			 */
+			OffsetNumber rnd_i, tmp;
+			rnd_i = random() % (maxoff - i) + i;
+			tmp = offsets[rnd_i];
+			offsets[rnd_i] = offsets[i];
+			offsets[i] = tmp;
+			offset = offsets[i];
+		}
+		else
+		{
+			/* No randomization: select next offset number */
+			offset = i + FirstOffsetNumber;
+		}
+
+		itup = (IndexTuple) PageGetItem(p, PageGetItemId(p, offset));
 
 		zero_penalty = true;
 
@@ -424,7 +457,7 @@ gistchoose(Relation r, Page p, IndexTuple it,	/* it has compressed entry */
 
 			/* Compute penalty for this column. */
 			datum = index_getattr(itup, j + 1, giststate->tupdesc, &IsNull);
-			gistdentryinit(giststate, j, &entry, datum, r, p, i,
+			gistdentryinit(giststate, j, &entry, datum, r, p, offset,
 						   FALSE, IsNull);
 			usize = gistpenalty(giststate, j, &entry, IsNull,
 								&identry[j], isnull[j]);
@@ -441,7 +474,7 @@ gistchoose(Relation r, Page p, IndexTuple it,	/* it has compressed entry */
 				 * adopt this tuple's penalty values as the best for all the
 				 * remaining columns during subsequent loop iterations.
 				 */
-				result = i;
+				result = offset;
 				best_penalty[j] = usize;
 
 				if (j < r->rd_att->natts - 1)