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.

1 files changed, 22 insertions, 52 deletions

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 64f5e5ad40a..4f6772564a8 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.164 2004/04/25 23:50:54 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.165 2004/05/08 19:09:25 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -98,8 +98,6 @@ static void write_buffer(Buffer buffer, bool unpin);
  *
  * Assume when this function is called, that reln has been
  *		opened already.
- *
- * Note: a side effect of a P_NEW call is to update reln->rd_nblocks.
  */
 Buffer
 ReadBuffer(Relation reln, BlockNumber blockNum)
@@ -129,14 +127,14 @@ ReadBufferInternal(Relation reln, BlockNumber blockNum,
 	if (reln->rd_smgr == NULL)
 		reln->rd_smgr = smgropen(reln->rd_node);
 
+	/* Substitute proper block number if caller asked for P_NEW */
+	if (isExtend)
+		blockNum = smgrnblocks(reln->rd_smgr);
+
 	if (isLocalBuf)
 	{
 		ReadLocalBufferCount++;
 		pgstat_count_buffer_read(&reln->pgstat_info, reln);
-		/* Substitute proper block number if caller asked for P_NEW */
-		if (isExtend)
-			blockNum = reln->rd_nblocks;
-
 		bufHdr = LocalBufferAlloc(reln, blockNum, &found);
 		if (found)
 			LocalBufferHitCount++;
@@ -145,13 +143,6 @@ ReadBufferInternal(Relation reln, BlockNumber blockNum,
 	{
 		ReadBufferCount++;
 		pgstat_count_buffer_read(&reln->pgstat_info, reln);
-		/* Substitute proper block number if caller asked for P_NEW */
-		if (isExtend)
-		{
-			/* must be sure we have accurate file length! */
-			blockNum = reln->rd_nblocks = smgrnblocks(reln->rd_smgr);
-		}
-
 		/*
 		 * lookup the buffer.  IO_IN_PROGRESS is set if the requested
 		 * block is not currently in memory.
@@ -196,8 +187,6 @@ ReadBufferInternal(Relation reln, BlockNumber blockNum,
 		/* new buffers are zero-filled */
 		MemSet((char *) MAKE_PTR(bufHdr->data), 0, BLCKSZ);
 		smgrextend(reln->rd_smgr, blockNum, (char *) MAKE_PTR(bufHdr->data));
-		/* After successful extend, increment relation length */
-		reln->rd_nblocks++;
 	}
 	else
 	{
@@ -1085,55 +1074,36 @@ FlushBuffer(BufferDesc *buf, SMgrRelation reln)
 /*
  * RelationGetNumberOfBlocks
  *		Determines the current number of pages in the relation.
- *		Side effect: relation->rd_nblocks is updated.
  */
 BlockNumber
 RelationGetNumberOfBlocks(Relation relation)
 {
-	/*
-	 * relation->rd_nblocks should be accurate already if the relation is
-	 * new or temp, because no one else should be modifying it.  Otherwise
-	 * we need to ask the smgr for the current physical file length.
-	 *
-	 * Don't call smgr on a view or a composite type, either.
-	 */
-	if (relation->rd_rel->relkind == RELKIND_VIEW ||
-		relation->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
-		relation->rd_nblocks = 0;
-	else if (!relation->rd_isnew && !relation->rd_istemp)
-	{
-		/* Open it at the smgr level if not already done */
-		if (relation->rd_smgr == NULL)
-			relation->rd_smgr = smgropen(relation->rd_node);
-
-		relation->rd_nblocks = smgrnblocks(relation->rd_smgr);
-	}
+	/* Open it at the smgr level if not already done */
+	if (relation->rd_smgr == NULL)
+		relation->rd_smgr = smgropen(relation->rd_node);
 
-	return relation->rd_nblocks;
+	return smgrnblocks(relation->rd_smgr);
 }
 
 /*
- * RelationUpdateNumberOfBlocks
- *		Forcibly update relation->rd_nblocks.
+ * RelationTruncate
+ *		Physically truncate a relation to the specified number of blocks.
  *
- * If the relcache drops an entry for a temp relation, it must call this
- * routine after recreating the relcache entry, so that rd_nblocks is
- * re-sync'd with reality.  See RelationGetNumberOfBlocks.
+ * Caller should already have done something to flush any buffered pages
+ * that are to be dropped.
  */
 void
-RelationUpdateNumberOfBlocks(Relation relation)
+RelationTruncate(Relation rel, BlockNumber nblocks)
 {
-	if (relation->rd_rel->relkind == RELKIND_VIEW ||
-		relation->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
-		relation->rd_nblocks = 0;
-	else
-	{
-		/* Open it at the smgr level if not already done */
-		if (relation->rd_smgr == NULL)
-			relation->rd_smgr = smgropen(relation->rd_node);
+	/* Open it at the smgr level if not already done */
+	if (rel->rd_smgr == NULL)
+		rel->rd_smgr = smgropen(rel->rd_node);
 
-		relation->rd_nblocks = smgrnblocks(relation->rd_smgr);
-	}
+	/* Make sure rd_targblock isn't pointing somewhere past end */
+	rel->rd_targblock = InvalidBlockNumber;
+
+	/* Do the real work */
+	smgrtruncate(rel->rd_smgr, nblocks);
 }
 
 /* ---------------------------------------------------------------------