Fix is-it-time-for-a-checkpoint logic so that checkpoint_segments can

usefully be larger than 255.  Per gripe from Simon Riggs.

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 8a94a62d48f86a555fe9e897b83596dab645ca57..68cf859587038e4c88e5d31af5a2a23c3d12e64b 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.178 2004/11/17 16:26:59 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.179 2004/12/17 00:10:36 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1201,21 +1201,38 @@ XLogWrite(XLogwrtRqst WriteRqst)
                UpdateControlFile();
 
                /*
-                * Signal postmaster to start a checkpoint if it's been
+                * Signal bgwriter to start a checkpoint if it's been
                 * too long since the last one.  (We look at local copy of
                 * RedoRecPtr which might be a little out of date, but
                 * should be close enough for this purpose.)
+                *
+                * A straight computation of segment number could overflow
+                * 32 bits.  Rather than assuming we have working 64-bit
+                * arithmetic, we compare the highest-order bits separately,
+                * and force a checkpoint immediately when they change.
                 */
-               if (IsUnderPostmaster &&
-                   (openLogId != RedoRecPtr.xlogid ||
-                    openLogSeg >= (RedoRecPtr.xrecoff / XLogSegSize) +
-                    (uint32) CheckPointSegments))
+               if (IsUnderPostmaster)
                {
+                   uint32      old_segno,
+                               new_segno;
+                   uint32      old_highbits,
+                               new_highbits;
+
+                   old_segno = (RedoRecPtr.xlogid % XLogSegSize) * XLogSegsPerFile +
+                       (RedoRecPtr.xrecoff / XLogSegSize);
+                   old_highbits = RedoRecPtr.xlogid / XLogSegSize;
+                   new_segno = (openLogId % XLogSegSize) * XLogSegsPerFile +
+                       openLogSeg;
+                   new_highbits = openLogId / XLogSegSize;
+                   if (new_highbits != old_highbits ||
+                       new_segno >= old_segno + (uint32) CheckPointSegments)
+                   {
 #ifdef WAL_DEBUG
-                   if (XLOG_DEBUG)
-                       elog(LOG, "time for a checkpoint, signaling bgwriter");
+                       if (XLOG_DEBUG)
+                           elog(LOG, "time for a checkpoint, signaling bgwriter");
 #endif
-                   RequestCheckpoint(false);
+                       RequestCheckpoint(false);
+                   }
                }
            }
            LWLockRelease(ControlFileLock);