Get rid of rd_nblocks field in relcache entries. Turns out this was

costing us lots more to maintain than it was worth.  On shared tables
it was of exactly zero benefit because we couldn't trust it to be
up to date.  On temp tables it sometimes saved an lseek, but not often
enough to be worth getting excited about.  And the real problem was that
we forced an lseek on every relcache flush in order to update the field.
So all in all it seems best to lose the complexity.

Author: tglsfdc

contrib/pgstattuple/pgstattuple.c

@@ -1,5 +1,5 @@
 /*
- * $PostgreSQL: pgsql/contrib/pgstattuple/pgstattuple.c,v 1.14 2004/04/01 21:28:43 tgl Exp $
+ * $PostgreSQL: pgsql/contrib/pgstattuple/pgstattuple.c,v 1.15 2004/05/08 19:09:24 tgl Exp $
  *
  * Copyright (c) 2001,2002	Tatsuo Ishii
  *
@@ -127,9 +127,10 @@ pgstattuple_real(Relation rel)
 	 */
 	attinmeta = TupleDescGetAttInMetadata(tupdesc);
 
-	nblocks = RelationGetNumberOfBlocks(rel);
 	scan = heap_beginscan(rel, SnapshotAny, 0, NULL);
 
+	nblocks = scan->rs_nblocks;	/* # blocks to be scanned */
+
 	/* scan the relation */
 	while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
 	{

src/backend/access/heap/heapam.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.165 2004/04/21 18:24:23 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.166 2004/05/08 19:09:24 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -73,12 +73,13 @@ static void
 initscan(HeapScanDesc scan, ScanKey key)
 {
 	/*
-	 * Make sure we have up-to-date idea of number of blocks in relation.
+	 * Determine the number of blocks we have to scan.
+	 *
 	 * It is sufficient to do this once at scan start, since any tuples
 	 * added while the scan is in progress will be invisible to my
 	 * transaction anyway...
 	 */
-	scan->rs_rd->rd_nblocks = RelationGetNumberOfBlocks(scan->rs_rd);
+	scan->rs_nblocks = RelationGetNumberOfBlocks(scan->rs_rd);
 
 	scan->rs_ctup.t_datamcxt = NULL;
 	scan->rs_ctup.t_data = NULL;
@@ -113,12 +114,12 @@ heapgettup(Relation relation,
 		   Buffer *buffer,
 		   Snapshot snapshot,
 		   int nkeys,
-		   ScanKey key)
+		   ScanKey key,
+		   BlockNumber pages)
 {
 	ItemId		lpp;
 	Page		dp;
 	BlockNumber page;
-	BlockNumber pages;
 	int			lines;
 	OffsetNumber lineoff;
 	int			linesleft;
@@ -159,7 +160,7 @@ heapgettup(Relation relation,
 	/*
 	 * return null immediately if relation is empty
 	 */
-	if ((pages = relation->rd_nblocks) == 0)
+	if (pages == 0)
 	{
 		if (BufferIsValid(*buffer))
 			ReleaseBuffer(*buffer);
@@ -832,7 +833,8 @@ heap_getnext(HeapScanDesc scan, ScanDirection direction)
 			   &(scan->rs_cbuf),
 			   scan->rs_snapshot,
 			   scan->rs_nkeys,
-			   scan->rs_key);
+			   scan->rs_key,
+			   scan->rs_nblocks);
 
 	if (scan->rs_ctup.t_data == NULL && !BufferIsValid(scan->rs_cbuf))
 	{
@@ -1992,7 +1994,8 @@ heap_restrpos(HeapScanDesc scan)
 				   &(scan->rs_cbuf),
 				   scan->rs_snapshot,
 				   0,
-				   NULL);
+				   NULL,
+				   scan->rs_nblocks);
 	}
 }
 

src/backend/access/nbtree/nbtree.c

@@ -12,7 +12,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.114 2004/04/21 18:24:26 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.115 2004/05/08 19:09:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -802,12 +802,7 @@ btvacuumcleanup(PG_FUNCTION_ARGS)
 			/*
 			 * Do the physical truncation.
 			 */
-			if (rel->rd_smgr == NULL)
-				rel->rd_smgr = smgropen(rel->rd_node);
-			new_pages = smgrtruncate(rel->rd_smgr, new_pages);
-			rel->rd_nblocks = new_pages;		/* update relcache
-												 * immediately */
-			rel->rd_targblock = InvalidBlockNumber;
+			RelationTruncate(rel, new_pages);
 			num_pages = new_pages;
 		}
 	}

src/backend/catalog/heap.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/catalog/heap.c,v 1.263 2004/05/05 04:48:45 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/catalog/heap.c,v 1.264 2004/05/08 19:09:24 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -1979,12 +1979,8 @@ RelationTruncateIndexes(Oid heapId)
 		 */
 		DropRelationBuffers(currentIndex);
 
-		/* Now truncate the actual data and set blocks to zero */
-		if (currentIndex->rd_smgr == NULL)
-			currentIndex->rd_smgr = smgropen(currentIndex->rd_node);
-		smgrtruncate(currentIndex->rd_smgr, 0);
-		currentIndex->rd_nblocks = 0;
-		currentIndex->rd_targblock = InvalidBlockNumber;
+		/* Now truncate the actual data */
+		RelationTruncate(currentIndex, 0);
 
 		/* Initialize the index and rebuild */
 		index_build(heapRelation, currentIndex, indexInfo);
@@ -2028,12 +2024,8 @@ heap_truncate(Oid rid)
 	 */
 	DropRelationBuffers(rel);
 
-	/* Now truncate the actual data and set blocks to zero */
-	if (rel->rd_smgr == NULL)
-		rel->rd_smgr = smgropen(rel->rd_node);
-	smgrtruncate(rel->rd_smgr, 0);
-	rel->rd_nblocks = 0;
-	rel->rd_targblock = InvalidBlockNumber;
+	/* Now truncate the actual data */
+	RelationTruncate(rel, 0);
 
 	/* If this relation has indexes, truncate the indexes too */
 	RelationTruncateIndexes(rid);

src/backend/catalog/index.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/catalog/index.c,v 1.230 2004/05/08 00:34:49 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/catalog/index.c,v 1.231 2004/05/08 19:09:24 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -1702,12 +1702,8 @@ reindex_index(Oid indexId)
 		 */
 		DropRelationBuffers(iRel);
 
-		/* Now truncate the actual data and set blocks to zero */
-		if (iRel->rd_smgr == NULL)
-			iRel->rd_smgr = smgropen(iRel->rd_node);
-		smgrtruncate(iRel->rd_smgr, 0);
-		iRel->rd_nblocks = 0;
-		iRel->rd_targblock = InvalidBlockNumber;
+		/* Now truncate the actual data */
+		RelationTruncate(iRel, 0);
 	}
 	else
 	{

src/backend/commands/analyze.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/analyze.c,v 1.70 2004/02/15 21:01:39 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/analyze.c,v 1.71 2004/05/08 19:09:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -388,15 +388,15 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt)
 
 	/*
 	 * If we are running a standalone ANALYZE, update pages/tuples stats
-	 * in pg_class.  We have the accurate page count from heap_beginscan,
+	 * in pg_class.  We know the accurate page count from the smgr,
 	 * but only an approximate number of tuples; therefore, if we are part
 	 * of VACUUM ANALYZE do *not* overwrite the accurate count already
 	 * inserted by VACUUM.  The same consideration applies to indexes.
 	 */
 	if (!vacstmt->vacuum)
 	{
 		vac_update_relstats(RelationGetRelid(onerel),
-							onerel->rd_nblocks,
+							RelationGetNumberOfBlocks(onerel),
 							totalrows,
 							hasindex);
 		for (ind = 0; ind < nindexes; ind++)
@@ -657,6 +657,7 @@ acquire_sample_rows(Relation onerel, HeapTuple *rows, int targrows,
 {
 	int			numrows = 0;
 	HeapScanDesc scan;
+	BlockNumber	totalblocks;
 	HeapTuple	tuple;
 	ItemPointer lasttuple;
 	BlockNumber lastblock,
@@ -673,6 +674,7 @@ acquire_sample_rows(Relation onerel, HeapTuple *rows, int targrows,
 	 * Do a simple linear scan until we reach the target number of rows.
 	 */
 	scan = heap_beginscan(onerel, SnapshotNow, 0, NULL);
+	totalblocks = scan->rs_nblocks;	/* grab current relation size */
 	while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
 	{
 		rows[numrows++] = heap_copytuple(tuple);
@@ -693,7 +695,7 @@ acquire_sample_rows(Relation onerel, HeapTuple *rows, int targrows,
 		ereport(elevel,
 				(errmsg("\"%s\": %u pages, %d rows sampled, %.0f estimated total rows",
 						RelationGetRelationName(onerel),
-						onerel->rd_nblocks, numrows, *totalrows)));
+						totalblocks, numrows, *totalrows)));
 
 		return numrows;
 	}
@@ -772,10 +774,9 @@ acquire_sample_rows(Relation onerel, HeapTuple *rows, int targrows,
 pageloop:;
 
 		/*
-		 * Have we fallen off the end of the relation?	(We rely on
-		 * heap_beginscan to have updated rd_nblocks.)
+		 * Have we fallen off the end of the relation?
 		 */
-		if (targblock >= onerel->rd_nblocks)
+		if (targblock >= totalblocks)
 			break;
 
 		/*
@@ -841,15 +842,15 @@ pageloop:;
 	/*
 	 * Estimate total number of valid rows in relation.
 	 */
-	*totalrows = floor((double) onerel->rd_nblocks * tuplesperpage + 0.5);
+	*totalrows = floor((double) totalblocks * tuplesperpage + 0.5);
 
 	/*
 	 * Emit some interesting relation info 
 	 */
 	ereport(elevel,
 			(errmsg("\"%s\": %u pages, %d rows sampled, %.0f estimated total rows",
 					RelationGetRelationName(onerel),
-					onerel->rd_nblocks, numrows, *totalrows)));
+					totalblocks, numrows, *totalrows)));
 
 	return numrows;
 }

src/backend/commands/sequence.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/sequence.c,v 1.109 2004/04/06 16:39:30 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/sequence.c,v 1.110 2004/05/08 19:09:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -822,10 +822,6 @@ read_info(SeqTable elm, Relation rel, Buffer *buf)
 	sequence_magic *sm;
 	Form_pg_sequence seq;
 
-	if (rel->rd_nblocks > 1)
-		elog(ERROR, "invalid number of blocks in sequence \"%s\"",
-			 RelationGetRelationName(rel));
-
 	*buf = ReadBuffer(rel, 0);
 	if (!BufferIsValid(*buf))
 		elog(ERROR, "ReadBuffer failed");

src/backend/commands/vacuum.c

@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.274 2004/02/12 05:39:55 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.275 2004/05/08 19:09:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2522,11 +2522,7 @@ repair_frag(VRelStats *vacrelstats, Relation onerel,
 	/* truncate relation, if needed */
 	if (blkno < nblocks)
 	{
-		if (onerel->rd_smgr == NULL)
-			onerel->rd_smgr = smgropen(onerel->rd_node);
-		blkno = smgrtruncate(onerel->rd_smgr, blkno);
-		onerel->rd_nblocks = blkno;		/* update relcache immediately */
-		onerel->rd_targblock = InvalidBlockNumber;
+		RelationTruncate(onerel, blkno);
 		vacrelstats->rel_pages = blkno; /* set new number of blocks */
 	}
 
@@ -2594,11 +2590,7 @@ vacuum_heap(VRelStats *vacrelstats, Relation onerel, VacPageList vacuum_pages)
 				(errmsg("\"%s\": truncated %u to %u pages",
 						RelationGetRelationName(onerel),
 						vacrelstats->rel_pages, relblocks)));
-		if (onerel->rd_smgr == NULL)
-			onerel->rd_smgr = smgropen(onerel->rd_node);
-		relblocks = smgrtruncate(onerel->rd_smgr, relblocks);
-		onerel->rd_nblocks = relblocks; /* update relcache immediately */
-		onerel->rd_targblock = InvalidBlockNumber;
+		RelationTruncate(onerel, relblocks);
 		vacrelstats->rel_pages = relblocks;		/* set new number of
 												 * blocks */
 	}

src/backend/commands/vacuumlazy.c

@@ -31,7 +31,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.39 2004/04/25 23:50:54 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.40 2004/05/08 19:09:25 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -738,11 +738,7 @@ lazy_truncate_heap(Relation onerel, LVRelStats *vacrelstats)
 	/*
 	 * Do the physical truncation.
 	 */
-	if (onerel->rd_smgr == NULL)
-		onerel->rd_smgr = smgropen(onerel->rd_node);
-	new_rel_pages = smgrtruncate(onerel->rd_smgr, new_rel_pages);
-	onerel->rd_nblocks = new_rel_pages; /* update relcache immediately */
-	onerel->rd_targblock = InvalidBlockNumber;
+	RelationTruncate(onerel, new_rel_pages);
 	vacrelstats->rel_pages = new_rel_pages;		/* save new number of
 												 * blocks */