Adjust WAL code so that checkpoints truncate the xlog at the previous

checkpoint's redo pointer, not its undo pointer, per discussion in
pghackers a few days ago.  No point in hanging onto undo information
until we have the ability to do something with it --- and this solves
a rather large problem with log space for long-running transactions.
Also, change all calls of write() to detect the case where write
returned a count less than requested, but failed to set errno.
Presume that this situation indicates ENOSPC, and give the appropriate
error message, rather than a random message associated with the previous
value of errno.

1 files changed, 8 insertions, 1 deletions

diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index 06ee4bc2729..237ae0a4428 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/file/fd.c,v 1.79 2001/05/30 14:15:26 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/file/fd.c,v 1.80 2001/06/06 17:07:46 tgl Exp $
  *
  * NOTES:
  *
@@ -865,7 +865,14 @@ FileWrite(File file, char *buffer, int amount)
 			   VfdCache[file].seekPos, amount, buffer));
 
 	FileAccess(file);
+
+	errno = 0;
 	returnCode = write(VfdCache[file].fd, buffer, amount);
+
+	/* if write didn't set errno, assume problem is no disk space */
+	if (returnCode != amount && errno == 0)
+		errno = ENOSPC;
+
 	if (returnCode > 0)
 		VfdCache[file].seekPos += returnCode;
 	else