Remove unnecessary calls of FlushRelationBuffers: there is no need

to write out data that we are about to tell the filesystem to drop.
smgr_internal_unlink already had a DropRelFileNodeBuffers call to
get rid of dead buffers without a write after it's no longer possible
to roll back the deleting transaction.  Adding a similar call in
smgrtruncate simplifies callers and makes the overall division of
labor clearer.  This patch removes the former behavior that VACUUM
would write all dirty buffers of a relation unconditionally.

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 1.124 2004/12/31 21:59:22 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtree.c,v 1.125 2005/03/20 22:00:50 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -772,17 +772,6 @@ btvacuumcleanup(PG_FUNCTION_ARGS)
 		{
 			/*
 			 * Okay to truncate.
-			 *
-			 * First, flush any shared buffers for the blocks we intend to
-			 * delete.	FlushRelationBuffers is a bit more than we need
-			 * for this, since it will also write out dirty buffers for
-			 * blocks we aren't deleting, but it's the closest thing in
-			 * bufmgr's API.
-			 */
-			FlushRelationBuffers(rel, new_pages);
-
-			/*
-			 * Do the physical truncation.
 			 */
 			RelationTruncate(rel, new_pages);
 

src/backend/catalog/heap.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/catalog/heap.c,v 1.280 2005/01/27 03:17:17 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/catalog/heap.c,v 1.281 2005/03/20 22:00:51 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -1174,12 +1174,6 @@ heap_drop_with_catalog(Oid relid)
 	 */
 	rel = relation_open(relid, AccessExclusiveLock);
 
-	/*
-	 * Release all buffers that belong to this relation, after writing any
-	 * that are dirty
-	 */
-	FlushRelationBuffers(rel, (BlockNumber) 0);
-
 	/*
 	 * Schedule unlinking of the relation's physical file at commit.
 	 */
@@ -1958,13 +1952,7 @@ RelationTruncateIndexes(Oid heapId)
 		/* Fetch info needed for index_build */
 		indexInfo = BuildIndexInfo(currentIndex);
 
-		/*
-		 * Drop any buffers associated with this index. If they're dirty,
-		 * they're just dropped without bothering to flush to disk.
-		 */
-		DropRelationBuffers(currentIndex);
-
-		/* Now truncate the actual data */
+		/* Now truncate the actual file (and discard buffers) */
 		RelationTruncate(currentIndex, 0);
 
 		/* Initialize the index and rebuild */
@@ -2024,13 +2012,7 @@ heap_truncate(List *relids)
 	{
 		Relation	rel = lfirst(cell);
 
-		/*
-		 * Release any buffers associated with this relation.  If they're
-		 * dirty, they're just dropped without bothering to flush to disk.
-		 */
-		DropRelationBuffers(rel);
-
-		/* Now truncate the actual data */
+		/* Truncate the actual file (and discard buffers) */
 		RelationTruncate(rel, 0);
 
 		/* If this relation has indexes, truncate the indexes too */

src/backend/catalog/index.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/catalog/index.c,v 1.247 2005/03/16 21:38:04 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/catalog/index.c,v 1.248 2005/03/20 22:00:51 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -775,10 +775,8 @@ index_drop(Oid indexId)
 	LockRelation(userIndexRelation, AccessExclusiveLock);
 
 	/*
-	 * flush buffer cache and schedule physical removal of the file
+	 * Schedule physical removal of the file
 	 */
-	FlushRelationBuffers(userIndexRelation, (BlockNumber) 0);
-
 	RelationOpenSmgr(userIndexRelation);
 	smgrscheduleunlink(userIndexRelation->rd_smgr,
 					   userIndexRelation->rd_istemp);
@@ -1617,14 +1615,7 @@ reindex_index(Oid indexId)
 
 		if (inplace)
 		{
-			/*
-			 * Release any buffers associated with this index.	If they're
-			 * dirty, they're just dropped without bothering to flush to
-			 * disk.
-			 */
-			DropRelationBuffers(iRel);
-
-			/* Now truncate the actual data */
+			/* Truncate the actual file (and discard buffers) */
 			RelationTruncate(iRel, 0);
 		}
 		else

src/backend/commands/cluster.c

@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/cluster.c,v 1.132 2005/02/06 20:19:08 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/cluster.c,v 1.133 2005/03/20 22:00:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -709,8 +709,7 @@ copy_heap_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex)
 void
 swap_relation_files(Oid r1, Oid r2)
 {
-	Relation	relRelation,
-				rel;
+	Relation	relRelation;
 	HeapTuple	reltup1,
 				reltup2;
 	Form_pg_class relform1,
@@ -735,20 +734,6 @@ swap_relation_files(Oid r1, Oid r2)
 		elog(ERROR, "cache lookup failed for relation %u", r2);
 	relform2 = (Form_pg_class) GETSTRUCT(reltup2);
 
-	/*
-	 * The buffer manager gets confused if we swap relfilenodes for
-	 * relations that are not both local or non-local to this transaction.
-	 * Flush the buffers on both relations so the buffer manager can
-	 * forget about'em.  (XXX this might not be necessary anymore?)
-	 */
-	rel = relation_open(r1, NoLock);
-	FlushRelationBuffers(rel, 0);
-	relation_close(rel, NoLock);
-
-	rel = relation_open(r2, NoLock);
-	FlushRelationBuffers(rel, 0);
-	relation_close(rel, NoLock);
-
 	/*
 	 * Actually swap the fields in the two tuples
 	 */

src/backend/commands/tablecmds.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.147 2005/03/16 21:38:05 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.148 2005/03/20 22:00:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -5628,13 +5628,12 @@ copy_relation_data(Relation rel, SMgrRelation dst)
 	Page		page = (Page) buf;
 
 	/*
-	 * Since we copy the data directly without looking at the shared
+	 * Since we copy the file directly without looking at the shared
 	 * buffers, we'd better first flush out any pages of the source
-	 * relation that are in shared buffers.  We assume no new pages will
-	 * get loaded into buffers while we are holding exclusive lock on the
-	 * rel.
+	 * relation that are in shared buffers.  We assume no new changes
+	 * will be made while we are holding exclusive lock on the rel.
 	 */
-	FlushRelationBuffers(rel, 0);
+	FlushRelationBuffers(rel);
 
 	/*
 	 * We need to log the copied data in WAL iff WAL archiving is enabled

src/backend/commands/vacuum.c

@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.304 2005/03/16 21:38:05 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.305 2005/03/20 22:00:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1138,16 +1138,6 @@ full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
 			/* Clean pages from vacuum_pages list */
 			vacuum_heap(vacrelstats, onerel, &vacuum_pages);
 		}
-		else
-		{
-			/*
-			 * Flush dirty pages out to disk.  We must do this even if we
-			 * didn't do anything else, because we want to ensure that all
-			 * tuples have correct on-row commit status on disk (see
-			 * bufmgr.c's comments for FlushRelationBuffers()).
-			 */
-			FlushRelationBuffers(onerel, vacrelstats->rel_pages);
-		}
 	}
 
 	/* update shared free space map with final free space info */
@@ -2420,15 +2410,7 @@ repair_frag(VRelStats *vacrelstats, Relation onerel,
 		pfree(Nvacpagelist.pagedesc);
 	}
 
-	/*
-	 * Flush dirty pages out to disk.  We do this unconditionally, even if
-	 * we don't need to truncate, because we want to ensure that all
-	 * tuples have correct on-row commit status on disk (see bufmgr.c's
-	 * comments for FlushRelationBuffers()).
-	 */
-	FlushRelationBuffers(onerel, blkno);
-
-	/* truncate relation, if needed */
+	/* Truncate relation, if needed */
 	if (blkno < nblocks)
 	{
 		RelationTruncate(onerel, blkno);
@@ -2818,27 +2800,17 @@ vacuum_heap(VRelStats *vacrelstats, Relation onerel, VacPageList vacuum_pages)
 		}
 	}
 
-	/*
-	 * Flush dirty pages out to disk.  We do this unconditionally, even if
-	 * we don't need to truncate, because we want to ensure that all
-	 * tuples have correct on-row commit status on disk (see bufmgr.c's
-	 * comments for FlushRelationBuffers()).
-	 */
+	/* Truncate relation if there are some empty end-pages */
 	Assert(vacrelstats->rel_pages >= vacuum_pages->empty_end_pages);
-	relblocks = vacrelstats->rel_pages - vacuum_pages->empty_end_pages;
-
-	FlushRelationBuffers(onerel, relblocks);
-
-	/* truncate relation if there are some empty end-pages */
 	if (vacuum_pages->empty_end_pages > 0)
 	{
+		relblocks = vacrelstats->rel_pages - vacuum_pages->empty_end_pages;
 		ereport(elevel,
 				(errmsg("\"%s\": truncated %u to %u pages",
 						RelationGetRelationName(onerel),
 						vacrelstats->rel_pages, relblocks)));
 		RelationTruncate(onerel, relblocks);
-		vacrelstats->rel_pages = relblocks;		/* set new number of
-												 * blocks */
+		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 1.50 2004/12/31 21:59:42 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.51 2005/03/20 22:00:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -773,16 +773,6 @@ lazy_truncate_heap(Relation onerel, LVRelStats *vacrelstats)
 
 	/*
 	 * Okay to truncate.
-	 *
-	 * First, flush any shared buffers for the blocks we intend to delete.
-	 * FlushRelationBuffers is a bit more than we need for this, since it
-	 * will also write out dirty buffers for blocks we aren't deleting,
-	 * but it's the closest thing in bufmgr's API.
-	 */
-	FlushRelationBuffers(onerel, new_rel_pages);
-
-	/*
-	 * Do the physical truncation.
 	 */
 	RelationTruncate(onerel, new_rel_pages);
 

src/backend/storage/smgr/smgr.c

@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/smgr/smgr.c,v 1.85 2005/01/10 20:02:22 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/smgr/smgr.c,v 1.86 2005/03/20 22:00:53 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -461,8 +461,8 @@ static void
 smgr_internal_unlink(RelFileNode rnode, int which, bool isTemp, bool isRedo)
 {
 	/*
-	 * Get rid of any leftover buffers for the rel (shouldn't be any in
-	 * the commit case, but there can be in the abort case).
+	 * Get rid of any remaining buffers for the relation.  bufmgr will just
+	 * drop them without bothering to write the contents.
 	 */
 	DropRelFileNodeBuffers(rnode, isTemp, 0);
 
@@ -599,6 +599,12 @@ smgrtruncate(SMgrRelation reln, BlockNumber nblocks, bool isTemp)
 {
 	BlockNumber newblks;
 
+	/*
+	 * Get rid of any buffers for the about-to-be-deleted blocks.
+	 * bufmgr will just drop them without bothering to write the contents.
+	 */
+	DropRelFileNodeBuffers(reln->smgr_rnode, isTemp, nblocks);
+
 	/*
 	 * Tell the free space map to forget anything it may have stored for
 	 * the about-to-be-deleted blocks.	We want to be sure it won't return
@@ -873,6 +879,8 @@ smgr_redo(XLogRecPtr lsn, XLogRecord *record)
 
 		reln = smgropen(xlrec->rnode);
 
+		/* Can't use smgrtruncate because it would try to xlog */
+
 		/*
 		 * First, force bufmgr to drop any buffers it has for the to-be-
 		 * truncated blocks.  We must do this, else subsequent
@@ -880,8 +888,6 @@ smgr_redo(XLogRecPtr lsn, XLogRecord *record)
 		 */
 		DropRelFileNodeBuffers(xlrec->rnode, false, xlrec->blkno);
 
-		/* Can't use smgrtruncate because it would try to xlog */
-
 		/*
 		 * Tell the free space map to forget anything it may have stored
 		 * for the about-to-be-deleted blocks.	We want to be sure it

src/include/storage/bufmgr.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/bufmgr.h,v 1.92 2005/03/19 23:27:10 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/storage/bufmgr.h,v 1.93 2005/03/20 22:00:54 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -132,8 +132,7 @@ extern void FlushBufferPool(void);
 extern BlockNumber BufferGetBlockNumber(Buffer buffer);
 extern BlockNumber RelationGetNumberOfBlocks(Relation relation);
 extern void RelationTruncate(Relation rel, BlockNumber nblocks);
-extern void FlushRelationBuffers(Relation rel, BlockNumber firstDelBlock);
-extern void DropRelationBuffers(Relation rel);
+extern void FlushRelationBuffers(Relation rel);
 extern void DropRelFileNodeBuffers(RelFileNode rnode, bool istemp,
 					   BlockNumber firstDelBlock);
 extern void DropBuffers(Oid dbid);