Make NOTIFY_PAYLOAD_MAX_LENGTH depend explicitly on BLCKSZ and

NAMEDATALEN, so this code doesn't go nuts with smaller than default
BLCKSZ or larger than default NAMEDATALEN.  The standard value is
still exactly 8000.

diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c
index f5863480f5e0b4a6877efd3cf0f5272ee7edf077..23c57cea04453303865503246c8ee0704ca5328f 100644 (file)
--- a/src/backend/commands/async.c
+++ b/src/backend/commands/async.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/commands/async.c,v 1.151 2010/02/16 22:34:43 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/commands/async.c,v 1.152 2010/02/17 00:52:09 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -137,9 +137,12 @@
 /*
  * Maximum size of a NOTIFY payload, including terminating NULL.  This
  * must be kept small enough so that a notification message fits on one
- * SLRU page.
+ * SLRU page.  The magic fudge factor here is noncritical as long as it's
+ * more than AsyncQueueEntryEmptySize --- we make it significantly bigger
+ * than that, so changes in that data structure won't affect user-visible
+ * restrictions.
  */
-#define NOTIFY_PAYLOAD_MAX_LENGTH      8000
+#define NOTIFY_PAYLOAD_MAX_LENGTH      (BLCKSZ - NAMEDATALEN - 128)
 
 /*
  * Struct representing an entry in the global notify queue