Adjust /contrib/pg_freespace to show index free space as NULL (FSM only

tracks index pages, not free space on pages):

1/ Index free bytes set to NULL
2/ Comment added to the README briefly mentioning the index business
3/ Columns reordered more logically
4/ 'Blockid' column removed
5/ Free bytes column renamed to just 'bytes' instead of 'blockfreebytes'

Mark Kirkwood

contrib/pg_freespacemap/README.pg_freespacemap

@@ -34,12 +34,12 @@ Notes
 
        Column     |  references          | Description
   ----------------+----------------------+------------------------------------
-   blockid        |                      | Id, 1.. max_fsm_pages
-   relfilenode    | pg_class.relfilenode | Refilenode of the relation.
    reltablespace  | pg_tablespace.oid    | Tablespace oid of the relation.
    reldatabase    | pg_database.oid      | Database for the relation.
+   relfilenode    | pg_class.relfilenode | Refilenode of the relation.
    relblocknumber |                      | Offset of the page in the relation.
-   blockfreebytes |                      | Free bytes in the block/page.
+   bytes          |                      | Free bytes in the block/page, or NULL
+                  |                      | for an index page (see below).
 
 
   There is one row for each page in the free space map.
@@ -47,6 +47,9 @@ Notes
   Because the map is shared by all the databases, there are pages from
   relations not belonging to the current database.
 
+  The free space map can contain pages for btree indexes if they were emptied 
+  by a vacuum process. The bytes field is set to NULL in this case.
+
   When the pg_freespacemap view is accessed, internal free space map locks are
   taken, and a copy of the map data is made for the view to display. 
   This ensures that the view produces a consistent set of results, while not 
@@ -60,22 +63,21 @@ Sample output
   regression=# \d pg_freespacemap
      View "public.pg_freespacemap"
       Column     |  Type   | Modifiers 
-  ---------------+---------+-----------
-  blockid        | integer | 
-  relfilenode    | oid     | 
+ ----------------+---------+-----------
   reltablespace  | oid     | 
   reldatabase    | oid     | 
+  relfilenode    | oid     | 
   relblocknumber | bigint  | 
-  blockfreebytes | integer | 
+  bytes          | integer | 
  View definition:
-  SELECT p.blockid, p.relfilenode, p.reltablespace, p.reldatabase, p.relblocknumber, p.blockfreebytes
-    FROM pg_freespacemap() p(blockid integer, relfilenode oid, reltablespace oid, reldatabase oid, relblocknumber bigint, blockfreebytes integer);
+ SELECT p.reltablespace, p.reldatabase, p.relfilenode, p.relblocknumber, p.bytes
+ FROM pg_freespacemap() p(reltablespace oid, reldatabase oid, relfilenode oid, relblocknumber bigint, bytes integer);
 
-  regression=# SELECT c.relname, m.relblocknumber, m.blockfreebytes  
+  regression=# SELECT c.relname, m.relblocknumber, m.bytes  
                FROM pg_freespacemap m INNER JOIN pg_class c 
                ON c.relfilenode = m.relfilenode LIMIT 10;
-      relname             | relblocknumber | blockfreebytes 
-  ------------------------+----------------+----------------
+      relname             | relblocknumber |  bytes 
+  ------------------------+----------------+--------
   sql_features            |              5 |   2696
   sql_implementation_info |              0 |   7104
   sql_languages           |              0 |   8016

contrib/pg_freespacemap/pg_freespacemap.c

@@ -3,7 +3,7 @@
  * pg_freespacemap.c
  *	  display some contents of the free space map.
  *
- *	  $PostgreSQL: pgsql/contrib/pg_freespacemap/pg_freespacemap.c,v 1.2 2006/02/14 15:03:59 tgl Exp $
+ *	  $PostgreSQL: pgsql/contrib/pg_freespacemap/pg_freespacemap.c,v 1.3 2006/04/26 22:41:18 momjian Exp $
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
@@ -12,7 +12,7 @@
 #include "storage/freespace.h"
 #include "utils/relcache.h"
 
-#define		NUM_FREESPACE_PAGES_ELEM 	6
+#define		NUM_FREESPACE_PAGES_ELEM 	5
 
 #if defined(WIN32) || defined(__CYGWIN__)
 /* Need DLLIMPORT for some things that are not so marked in main headers */
@@ -29,12 +29,12 @@ Datum		pg_freespacemap(PG_FUNCTION_ARGS);
 typedef struct
 {
 
-	uint32				blockid;
-	uint32				relfilenode;
 	uint32				reltablespace;
 	uint32				reldatabase;
+	uint32				relfilenode;
 	uint32				relblocknumber;
-	uint32				blockfreebytes;
+	uint32				bytes;
+	bool				isindex;
 
 }	FreeSpacePagesRec;
 
@@ -91,17 +91,15 @@ pg_freespacemap(PG_FUNCTION_ARGS)
 
 		/* Construct a tuple to return. */
 		tupledesc = CreateTemplateTupleDesc(NUM_FREESPACE_PAGES_ELEM, false);
-		TupleDescInitEntry(tupledesc, (AttrNumber) 1, "blockid",
-						   INT4OID, -1, 0);
-		TupleDescInitEntry(tupledesc, (AttrNumber) 2, "relfilenode",
+		TupleDescInitEntry(tupledesc, (AttrNumber) 1, "reltablespace",
 						   OIDOID, -1, 0);
-		TupleDescInitEntry(tupledesc, (AttrNumber) 3, "reltablespace",
+		TupleDescInitEntry(tupledesc, (AttrNumber) 2, "reldatabase",
 						   OIDOID, -1, 0);
-		TupleDescInitEntry(tupledesc, (AttrNumber) 4, "reldatabase",
+		TupleDescInitEntry(tupledesc, (AttrNumber) 3, "relfilenode",
 						   OIDOID, -1, 0);
-		TupleDescInitEntry(tupledesc, (AttrNumber) 5, "relblocknumber",
+		TupleDescInitEntry(tupledesc, (AttrNumber) 4, "relblocknumber",
 						   INT8OID, -1, 0);
-		TupleDescInitEntry(tupledesc, (AttrNumber) 6, "blockfreebytes",
+		TupleDescInitEntry(tupledesc, (AttrNumber) 5, "bytes",
 						   INT4OID, -1, 0);
 
 		/* Generate attribute metadata needed later to produce tuples */
@@ -129,7 +127,6 @@ pg_freespacemap(PG_FUNCTION_ARGS)
 		fctx->values[2] = (char *) palloc(3 * sizeof(uint32) + 1);
 		fctx->values[3] = (char *) palloc(3 * sizeof(uint32) + 1);
 		fctx->values[4] = (char *) palloc(3 * sizeof(uint32) + 1);
-		fctx->values[5] = (char *) palloc(3 * sizeof(uint32) + 1);
 
 
 		/* Return to original context when allocating transient memory */
@@ -158,12 +155,12 @@ pg_freespacemap(PG_FUNCTION_ARGS)
 				for (nPages = 0; nPages < fsmrel->storedPages; nPages++)
 				{
 
-					fctx->record[i].blockid = i;
-					fctx->record[i].relfilenode = fsmrel->key.relNode;
 					fctx->record[i].reltablespace = fsmrel->key.spcNode;
 					fctx->record[i].reldatabase = fsmrel->key.dbNode;
+					fctx->record[i].relfilenode = fsmrel->key.relNode;
 					fctx->record[i].relblocknumber = IndexFSMPageGetPageNum(page);	
-					fctx->record[i].blockfreebytes = 0;	/* index.*/
+					fctx->record[i].bytes = 0;	
+					fctx->record[i].isindex = true;	
 
 					page++;
 					i++;
@@ -178,12 +175,12 @@ pg_freespacemap(PG_FUNCTION_ARGS)
 
 				for (nPages = 0; nPages < fsmrel->storedPages; nPages++)
 				{
-					fctx->record[i].blockid = i;
-					fctx->record[i].relfilenode = fsmrel->key.relNode;
 					fctx->record[i].reltablespace = fsmrel->key.spcNode;
 					fctx->record[i].reldatabase = fsmrel->key.dbNode;
+					fctx->record[i].relfilenode = fsmrel->key.relNode;
 					fctx->record[i].relblocknumber = FSMPageGetPageNum(page);
-					fctx->record[i].blockfreebytes = FSMPageGetSpace(page);	
+					fctx->record[i].bytes = FSMPageGetSpace(page);	
+					fctx->record[i].isindex = false;	
 					
 					page++;
 					i++;
@@ -209,19 +206,41 @@ pg_freespacemap(PG_FUNCTION_ARGS)
 	if (funcctx->call_cntr < funcctx->max_calls)
 	{
 		uint32		i = funcctx->call_cntr;
+		char		*values[NUM_FREESPACE_PAGES_ELEM];
+		int			j;
 
+		/*
+		 * Use a temporary values array, initially pointing to fctx->values,
+		 * so it can be reassigned w/o losing the storage for subsequent
+		 * calls.
+		 */
+		for (j = 0; j < NUM_FREESPACE_PAGES_ELEM; j++)
+		{
+			values[j] = fctx->values[j];
+		}
+
+
+		sprintf(values[0], "%u", fctx->record[i].reltablespace);
+		sprintf(values[1], "%u", fctx->record[i].reldatabase);
+		sprintf(values[2], "%u", fctx->record[i].relfilenode);
+		sprintf(values[3], "%u", fctx->record[i].relblocknumber);
 
-		sprintf(fctx->values[0], "%u", fctx->record[i].blockid);
-		sprintf(fctx->values[1], "%u", fctx->record[i].relfilenode);
-		sprintf(fctx->values[2], "%u", fctx->record[i].reltablespace);
-		sprintf(fctx->values[3], "%u", fctx->record[i].reldatabase);
-		sprintf(fctx->values[4], "%u", fctx->record[i].relblocknumber);
-		sprintf(fctx->values[5], "%u", fctx->record[i].blockfreebytes);
 
+		/*
+		 * Set (free) bytes to NULL for an index relation.
+		 */
+		if (fctx->record[i].isindex == true)
+		{
+			values[4] = NULL;
+		}
+		else
+		{
+			sprintf(values[4], "%u", fctx->record[i].bytes);
+		}
 
 
 		/* Build and return the tuple. */
-		tuple = BuildTupleFromCStrings(funcctx->attinmeta, fctx->values);
+		tuple = BuildTupleFromCStrings(funcctx->attinmeta, values);
 		result = HeapTupleGetDatum(tuple);
 
 

contrib/pg_freespacemap/pg_freespacemap.sql.in

@@ -11,7 +11,7 @@ LANGUAGE C;
 -- Create a view for convenient access.
 CREATE VIEW pg_freespacemap AS
 	SELECT P.* FROM pg_freespacemap() AS P
- 	(blockid int4, relfilenode oid, reltablespace oid, reldatabase oid, relblocknumber int8, blockfreebytes int4);
+ 	(reltablespace oid, reldatabase oid, relfilenode oid, relblocknumber int8, bytes int4);
  
 -- Don't want these to be available at public.
 REVOKE ALL ON FUNCTION pg_freespacemap() FROM PUBLIC;