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/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);