Rewrite the FSM. Instead of relying on a fixed-size shared memory segment, the

free space information is stored in a dedicated FSM relation fork, with each
relation (except for hash indexes; they don't use FSM).

This eliminates the max_fsm_relations and max_fsm_pages GUC options; remove any
trace of them from the backend, initdb, and documentation.

Rewrite contrib/pg_freespacemap to match the new FSM implementation. Also
introduce a new variant of the get_raw_page(regclass, int4, int4) function in
contrib/pageinspect that let's you to return pages from any relation fork, and
a new fsm_page_contents() function to inspect the new FSM pages.

1 files changed, 92 insertions, 0 deletions

diff --git a/src/backend/storage/freespace/indexfsm.c b/src/backend/storage/freespace/indexfsm.c
new file mode 100644
index 00000000000..62fd3d37942
--- /dev/null
+++ b/src/backend/storage/freespace/indexfsm.c
@@ -0,0 +1,92 @@
+/*-------------------------------------------------------------------------
+ *
+ * indexfsm.c
+ *	  POSTGRES free space map for quickly finding free pages in relations
+ *
+ *
+ * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  $PostgreSQL: pgsql/src/backend/storage/freespace/indexfsm.c,v 1.1 2008/09/30 10:52:13 heikki Exp $
+ *
+ *
+ * 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"
+#include "storage/smgr.h"
+
+/*
+ * Exported routines
+ */
+
+/*
+ * InitIndexFreeSpaceMap - Create or reset the FSM fork for relation.
+ */
+void
+InitIndexFreeSpaceMap(Relation rel)
+{
+	/* Create FSM fork if it doesn't exist yet, or truncate it if it does */
+	RelationOpenSmgr(rel);
+	if (!smgrexists(rel->rd_smgr, FSM_FORKNUM))
+		smgrcreate(rel->rd_smgr, FSM_FORKNUM, rel->rd_istemp, false);
+	else
+		smgrtruncate(rel->rd_smgr, FSM_FORKNUM, 0, rel->rd_istemp);
+}
+
+/*
+ * 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);
+}
+
+/*
+ * IndexFreeSpaceMapTruncate - adjust for truncation of a relation.
+ *
+ * We need to delete any stored data past the new relation length, so that
+ * we don't bogusly return removed block numbers.
+ */
+void
+IndexFreeSpaceMapTruncate(Relation rel, BlockNumber nblocks)
+{
+	FreeSpaceMapTruncateRel(rel, nblocks);
+}