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diff --git a/src/backend/storage/freespace/indexfsm.c b/src/backend/storage/freespace/indexfsm.c
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index 0000000..d66e10b
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+++ b/src/backend/storage/freespace/indexfsm.c
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+/*-------------------------------------------------------------------------
+ *
+ * indexfsm.c
+ *	  POSTGRES free space map for quickly finding free pages in relations
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/storage/freespace/indexfsm.c
+ *
+ *
+ * NOTES:
+ *
+ *	This is similar to the FSM used for heap, in freespace.c, but instead
+ *	of tracking the amount of free space on pages, we only track whether
+ *	pages are completely free or in-use. We use the same FSM implementation
+ *	as for heaps, using BLCKSZ - 1 to denote used pages, and 0 for unused.
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "storage/freespace.h"
+#include "storage/indexfsm.h"
+
+/*
+ * Exported routines
+ */
+
+/*
+ * GetFreeIndexPage - return a free page from the FSM
+ *
+ * As a side effect, the page is marked as used in the FSM.
+ */
+BlockNumber
+GetFreeIndexPage(Relation rel)
+{
+	BlockNumber blkno = GetPageWithFreeSpace(rel, BLCKSZ / 2);
+
+	if (blkno != InvalidBlockNumber)
+		RecordUsedIndexPage(rel, blkno);
+
+	return blkno;
+}
+
+/*
+ * RecordFreeIndexPage - mark a page as free in the FSM
+ */
+void
+RecordFreeIndexPage(Relation rel, BlockNumber freeBlock)
+{
+	RecordPageWithFreeSpace(rel, freeBlock, BLCKSZ - 1);
+}
+
+
+/*
+ * RecordUsedIndexPage - mark a page as used in the FSM
+ */
+void
+RecordUsedIndexPage(Relation rel, BlockNumber usedBlock)
+{
+	RecordPageWithFreeSpace(rel, usedBlock, 0);
+}
+
+/*
+ * IndexFreeSpaceMapVacuum - scan and fix any inconsistencies in the FSM
+ */
+void
+IndexFreeSpaceMapVacuum(Relation rel)
+{
+	FreeSpaceMapVacuum(rel);
+}