Make NOTIFY_PAYLOAD_MAX_LENGTH depend explicitly on BLCKSZ and

tglsfdc · tglsfdc · commit ee678fe30c3b · 2010-02-17T00:52:09.000Z
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
@@ -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
