Clean up WAL/buffer interactions as per my recent proposal. Get rid of the

misleadingly-named WriteBuffer routine, and instead require routines that
change buffer pages to call MarkBufferDirty (which does exactly what it says).
We also require that they do so before calling XLogInsert; this takes care of
the synchronization requirement documented in SyncOneBuffer.  Note that
because bufmgr takes the buffer content lock (in shared mode) while writing
out any buffer, it doesn't matter whether MarkBufferDirty is executed before
the buffer content change is complete, so long as the content change is
completed before releasing exclusive lock on the buffer.  So it's OK to set
the dirtybit before we fill in the LSN.
This eliminates the former kluge of needing to set the dirtybit in LockBuffer.
Aside from making the code more transparent, we can also add some new
debugging assertions, in particular that the caller of MarkBufferDirty must
hold the buffer content lock, not merely a pin.

1 files changed, 5 insertions, 5 deletions

diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c
index fb771fe2fd1..1ab4095350a 100644
--- a/src/backend/access/transam/xlogutils.c
+++ b/src/backend/access/transam/xlogutils.c
@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlogutils.c,v 1.42 2006/03/29 21:17:38 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlogutils.c,v 1.43 2006/03/31 23:32:06 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -30,9 +30,9 @@
  *
  * This is functionally comparable to ReadBuffer followed by
  * LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE): you get back a pinned
- * and locked buffer.  (The lock is not really necessary, since we
- * expect that this is only done during single-process XLOG replay,
- * but in some places it simplifies sharing code with the non-XLOG case.)
+ * and locked buffer.  (Getting the lock is not really necessary, since we
+ * expect that this is only used during single-process XLOG replay, but
+ * some subroutines such as MarkBufferDirty will complain if we don't.)
  *
  * If "init" is true then the caller intends to rewrite the page fully
  * using the info in the XLOG record.  In this case we will extend the
@@ -74,7 +74,7 @@ XLogReadBuffer(Relation reln, BlockNumber blkno, bool init)
 		while (blkno >= lastblock)
 		{
 			if (buffer != InvalidBuffer)
-				ReleaseBuffer(buffer);		/* must be WriteBuffer()? */
+				ReleaseBuffer(buffer);
 			buffer = ReadBuffer(reln, P_NEW);
 			lastblock++;
 		}