Rewrite the sinval messaging mechanism to reduce contention and avoid

unnecessary cache resets.  The major changes are:

* When the queue overflows, we only issue a cache reset to the specific
backend or backends that still haven't read the oldest message, rather
than resetting everyone as in the original coding.

* When we observe backend(s) falling well behind, we signal SIGUSR1
to only one backend, the one that is furthest behind and doesn't already
have a signal outstanding for it.  When it finishes catching up, it will
in turn signal SIGUSR1 to the next-furthest-back guy, if there is one that
is far enough behind to justify a signal.  The PMSIGNAL_WAKEN_CHILDREN
mechanism is removed.

* We don't attempt to clean out dead messages after every message-receipt
operation; rather, we do it on the insertion side, and only when the queue
fullness passes certain thresholds.

* Split SInvalLock into SInvalReadLock and SInvalWriteLock so that readers
don't block writers nor vice versa (except during the infrequent queue
cleanout operations).

* Transfer multiple sinval messages for each acquisition of a read or
write lock.

4 files changed, 14 insertions, 13 deletions

diff --git a/src/include/storage/lwlock.h b/src/include/storage/lwlock.h
index baccfbf5a68..b1088fcd33d 100644
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/lwlock.h,v 1.38 2008/01/01 19:45:59 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/storage/lwlock.h,v 1.39 2008/06/19 21:32:56 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -43,7 +43,8 @@ typedef enum LWLockId
 	OidGenLock,
 	XidGenLock,
 	ProcArrayLock,
-	SInvalLock,
+	SInvalReadLock,
+	SInvalWriteLock,
 	FreeSpaceLock,
 	WALInsertLock,
 	WALWriteLock,
diff --git a/src/include/storage/pmsignal.h b/src/include/storage/pmsignal.h
index c02593e5a86..94f1770ffce 100644
--- a/src/include/storage/pmsignal.h
+++ b/src/include/storage/pmsignal.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/pmsignal.h,v 1.19 2008/01/01 19:45:59 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/storage/pmsignal.h,v 1.20 2008/06/19 21:32:56 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -23,7 +23,6 @@
 typedef enum
 {
 	PMSIGNAL_PASSWORD_CHANGE,	/* pg_auth file has changed */
-	PMSIGNAL_WAKEN_CHILDREN,	/* send a SIGUSR1 signal to all backends */
 	PMSIGNAL_WAKEN_ARCHIVER,	/* send a NOTIFY signal to xlog archiver */
 	PMSIGNAL_ROTATE_LOGFILE,	/* send SIGUSR1 to syslogger to rotate logfile */
 	PMSIGNAL_START_AUTOVAC_LAUNCHER,	/* start an autovacuum launcher */
diff --git a/src/include/storage/sinval.h b/src/include/storage/sinval.h
index 343c8d94bdb..3601216f1b6 100644
--- a/src/include/storage/sinval.h
+++ b/src/include/storage/sinval.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/sinval.h,v 1.47 2008/03/16 19:47:34 alvherre Exp $
+ * $PostgreSQL: pgsql/src/include/storage/sinval.h,v 1.48 2008/06/19 21:32:56 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -83,7 +83,8 @@ typedef union
 } SharedInvalidationMessage;
 
 
-extern void SendSharedInvalidMessage(SharedInvalidationMessage *msg);
+extern void SendSharedInvalidMessages(const SharedInvalidationMessage *msgs,
+									  int n);
 extern void ReceiveSharedInvalidMessages(
 					  void (*invalFunction) (SharedInvalidationMessage *msg),
 							 void (*resetFunction) (void));
diff --git a/src/include/storage/sinvaladt.h b/src/include/storage/sinvaladt.h
index 8535cba0f06..1748f8821b4 100644
--- a/src/include/storage/sinvaladt.h
+++ b/src/include/storage/sinvaladt.h
@@ -1,12 +1,13 @@
 /*-------------------------------------------------------------------------
  *
  * sinvaladt.h
- *	  POSTGRES shared cache invalidation segment definitions.
+ *	  POSTGRES shared cache invalidation data manager.
  *
  * The shared cache invalidation manager is responsible for transmitting
  * invalidation messages between backends.	Any message sent by any backend
  * must be delivered to all already-running backends before it can be
- * forgotten.
+ * forgotten.  (If we run out of space, we instead deliver a "RESET"
+ * message to backends that have fallen too far behind.)
  * 
  * The struct type SharedInvalidationMessage, defining the contents of
  * a single message, is defined in sinval.h.
@@ -14,7 +15,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/sinvaladt.h,v 1.47 2008/03/17 11:50:27 alvherre Exp $
+ * $PostgreSQL: pgsql/src/include/storage/sinvaladt.h,v 1.48 2008/06/19 21:32:56 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -23,7 +24,6 @@
 
 #include "storage/sinval.h"
 
-
 /*
  * prototypes for functions in sinvaladt.c
  */
@@ -31,9 +31,9 @@ extern Size SInvalShmemSize(void);
 extern void CreateSharedInvalidationState(void);
 extern void SharedInvalBackendInit(void);
 
-extern bool SIInsertDataEntry(SharedInvalidationMessage *data);
-extern int SIGetDataEntry(int backendId, SharedInvalidationMessage *data);
-extern void SIDelExpiredDataEntries(bool locked);
+extern void SIInsertDataEntries(const SharedInvalidationMessage *data, int n);
+extern int SIGetDataEntries(SharedInvalidationMessage *data, int datasize);
+extern void SICleanupQueue(bool callerHasWriteLock, int minFree);
 
 extern LocalTransactionId GetNextLocalTransactionId(void);