1 files changed, 42 insertions, 0 deletions
diff --git a/contrib/pg_freespacemap/pg_freespacemap.c b/contrib/pg_freespacemap/pg_freespacemap.c
new file mode 100644
index 0000000..b82cab2
--- /dev/null
+++ b/contrib/pg_freespacemap/pg_freespacemap.c
@@ -0,0 +1,42 @@
+/*-------------------------------------------------------------------------
+ *
+ * pg_freespacemap.c
+ *	  display contents of a free space map
+ *
+ *	  contrib/pg_freespacemap/pg_freespacemap.c
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/relation.h"
+#include "funcapi.h"
+#include "storage/freespace.h"
+
+PG_MODULE_MAGIC;
+
+/*
+ * Returns the amount of free space on a given page, according to the
+ * free space map.
+ */
+PG_FUNCTION_INFO_V1(pg_freespace);
+
+Datum
+pg_freespace(PG_FUNCTION_ARGS)
+{
+	Oid			relid = PG_GETARG_OID(0);
+	int64		blkno = PG_GETARG_INT64(1);
+	int16		freespace;
+	Relation	rel;
+
+	rel = relation_open(relid, AccessShareLock);
+
+	if (blkno < 0 || blkno > MaxBlockNumber)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("invalid block number")));
+
+	freespace = GetRecordedFreeSpace(rel, blkno);
+
+	relation_close(rel, AccessShareLock);
+	PG_RETURN_INT16(freespace);
+}