Replace the pg_listener-based LISTEN/NOTIFY mechanism with an in-memory queue.

In addition, add support for a "payload" string to be passed along with
each notify event.

This implementation should be significantly more efficient than the old one,
and is also more compatible with Hot Standby usage.  There is not yet any
facility for HS slaves to receive notifications generated on the master,
although such a thing is possible in future.

Joachim Wieland, reviewed by Jeff Davis; also hacked on by me.

1 files changed, 3 insertions, 20 deletions

diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c
index d5f999f494b..6226acc9283 100644
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -41,7 +41,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/slru.c,v 1.48 2010/01/02 16:57:35 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/slru.c,v 1.49 2010/02/16 22:34:43 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -59,25 +59,6 @@
 #include "miscadmin.h"
 
 
-/*
- * Define segment size.  A page is the same BLCKSZ as is used everywhere
- * else in Postgres.  The segment size can be chosen somewhat arbitrarily;
- * we make it 32 pages by default, or 256Kb, i.e. 1M transactions for CLOG
- * or 64K transactions for SUBTRANS.
- *
- * Note: because TransactionIds are 32 bits and wrap around at 0xFFFFFFFF,
- * page numbering also wraps around at 0xFFFFFFFF/xxxx_XACTS_PER_PAGE (where
- * xxxx is CLOG or SUBTRANS, respectively), and segment numbering at
- * 0xFFFFFFFF/xxxx_XACTS_PER_PAGE/SLRU_PAGES_PER_SEGMENT.  We need
- * take no explicit notice of that fact in this module, except when comparing
- * segment and page numbers in SimpleLruTruncate (see PagePrecedes()).
- *
- * Note: this file currently assumes that segment file names will be four
- * hex digits.	This sets a lower bound on the segment size (64K transactions
- * for 32-bit TransactionIds).
- */
-#define SLRU_PAGES_PER_SEGMENT	32
-
 #define SlruFileName(ctl, path, seg) \
 	snprintf(path, MAXPGPATH, "%s/%04X", (ctl)->Dir, seg)
 
@@ -183,6 +164,8 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
 	shared = (SlruShared) ShmemInitStruct(name,
 										  SimpleLruShmemSize(nslots, nlsns),
 										  &found);
+	if (!shared)
+		elog(ERROR, "out of shared memory");
 
 	if (!IsUnderPostmaster)
 	{