Bloom index contrib module

Module provides new access method. It is actually a simple Bloom filter
implemented as pgsql's index. It could give some benefits on search
with large number of columns.

Module is a single way to test generic WAL interface committed earlier.

Author: Teodor Sigaev, Alexander Korotkov
Reviewers: Aleksander Alekseev, Michael Paquier, Jim Nasby

contrib/bloom/blcost.c

@@ -0,0 +1,48 @@
+/*-------------------------------------------------------------------------
+ *
+ * blcost.c
+ *		Cost estimate function for bloom indexes.
+ *
+ * Copyright (c) 2016, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  contrib/bloom/blcost.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "fmgr.h"
+#include "optimizer/cost.h"
+#include "utils/selfuncs.h"
+
+#include "bloom.h"
+
+/*
+ * Estimate cost of bloom index scan.
+ */
+void
+blcostestimate(PlannerInfo *root, IndexPath *path, double loop_count,
+			   Cost *indexStartupCost, Cost *indexTotalCost,
+			   Selectivity *indexSelectivity, double *indexCorrelation)
+{
+	IndexOptInfo *index = path->indexinfo;
+	List	   *qinfos;
+	GenericCosts costs;
+
+	/* Do preliminary analysis of indexquals */
+	qinfos = deconstruct_indexquals(path);
+
+	MemSet(&costs, 0, sizeof(costs));
+
+	/* We have to visit all index tuples anyway */
+	costs.numIndexTuples = index->tuples;
+
+	/* Use generic estimate */
+	genericcostestimate(root, path, loop_count, qinfos, &costs);
+
+	*indexStartupCost = costs.indexStartupCost;
+	*indexTotalCost = costs.indexTotalCost;
+	*indexSelectivity = costs.indexSelectivity;
+	*indexCorrelation = costs.indexCorrelation;
+}