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diff --git a/src/backend/optimizer/geqo/geqo_selection.c b/src/backend/optimizer/geqo/geqo_selection.c
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+/*-------------------------------------------------------------------------
+ *
+ * geqo_selection.c
+ *	  linear selection scheme for the genetic query optimizer
+ *
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/backend/optimizer/geqo/geqo_selection.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+/* contributed by:
+   =*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
+   *  Martin Utesch				 * Institute of Automatic Control	   *
+   =							 = University of Mining and Technology =
+   *  utesch@aut.tu-freiberg.de  * Freiberg, Germany				   *
+   =*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
+ */
+
+/* this is adopted from D. Whitley's Genitor algorithm */
+
+/*************************************************************/
+/*															 */
+/*	Copyright (c) 1990										 */
+/*	Darrell L. Whitley										 */
+/*	Computer Science Department								 */
+/*	Colorado State University								 */
+/*															 */
+/*	Permission is hereby granted to copy all or any part of  */
+/*	this program for free distribution.   The author's name  */
+/*	and this copyright notice must be included in any copy.  */
+/*															 */
+/*************************************************************/
+
+#include "postgres.h"
+
+#include <math.h>
+
+#include "optimizer/geqo_copy.h"
+#include "optimizer/geqo_random.h"
+#include "optimizer/geqo_selection.h"
+
+static int	linear_rand(PlannerInfo *root, int max, double bias);
+
+
+/*
+ * geqo_selection
+ *	 according to bias described by input parameters,
+ *	 first and second genes are selected from the pool
+ */
+void
+geqo_selection(PlannerInfo *root, Chromosome *momma, Chromosome *daddy,
+			   Pool *pool, double bias)
+{
+	int			first,
+				second;
+
+	first = linear_rand(root, pool->size, bias);
+	second = linear_rand(root, pool->size, bias);
+
+	/*
+	 * Ensure we have selected different genes, except if pool size is only
+	 * one, when we can't.
+	 */
+	if (pool->size > 1)
+	{
+		while (first == second)
+			second = linear_rand(root, pool->size, bias);
+	}
+
+	geqo_copy(root, momma, &pool->data[first], pool->string_length);
+	geqo_copy(root, daddy, &pool->data[second], pool->string_length);
+}
+
+/*
+ * linear_rand
+ *	  generates random integer between 0 and input max number
+ *	  using input linear bias
+ *
+ *	  bias is y-intercept of linear distribution
+ *
+ *	  probability distribution function is: f(x) = bias - 2(bias - 1)x
+ *			 bias = (prob of first rule) / (prob of middle rule)
+ */
+static int
+linear_rand(PlannerInfo *root, int pool_size, double bias)
+{
+	double		index;			/* index between 0 and pool_size */
+	double		max = (double) pool_size;
+
+	/*
+	 * geqo_rand() is not supposed to return 1.0, but if it does then we will
+	 * get exactly max from this equation, whereas we need 0 <= index < max.
+	 * Also it seems possible that roundoff error might deliver values
+	 * slightly outside the range; in particular avoid passing a value
+	 * slightly less than 0 to sqrt().  If we get a bad value just try again.
+	 */
+	do
+	{
+		double		sqrtval;
+
+		sqrtval = (bias * bias) - 4.0 * (bias - 1.0) * geqo_rand(root);
+		if (sqrtval > 0.0)
+			sqrtval = sqrt(sqrtval);
+		index = max * (bias - sqrtval) / 2.0 / (bias - 1.0);
+	} while (index < 0.0 || index >= max);
+
+	return (int) index;
+}