I finally understood what sinvaladt.c is doing --- and it

offended my aesthestic sensibility that there was so much unreadable code
doing so little.  Rewritten code is about half the size, faster, and
(I hope) much more intelligible.

src/backend/storage/ipc/sinval.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/sinval.c,v 1.17 1999/09/04 18:36:45 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/sinval.c,v 1.18 1999/09/06 19:37:38 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -21,12 +21,6 @@
 #include "storage/sinval.h"
 #include "storage/sinvaladt.h"
 
-extern SISeg *shmInvalBuffer;	/* the shared buffer segment, set by
-								 * SISegmentAttach()
-								 */
-extern BackendId MyBackendId;
-extern BackendTag MyBackendTag;
-
 SPINLOCK	SInvalLock = (SPINLOCK) NULL;
 
 /****************************************************************************/
@@ -39,11 +33,6 @@ CreateSharedInvalidationState(IPCKey key, int maxBackends)
 {
 	int			status;
 
-	/*
-	 * REMOVED SISyncKill(IPCKeyGetSIBufferMemorySemaphoreKey(key));
-	 * SISyncInit(IPCKeyGetSIBufferMemorySemaphoreKey(key));
-	 */
-
 	/* SInvalLock gets set in spin.c, during spinlock init */
 	status = SISegmentInit(true, IPCKeyGetSIBufferMemoryBlock(key),
 						   maxBackends);
@@ -53,9 +42,9 @@ CreateSharedInvalidationState(IPCKey key, int maxBackends)
 }
 
 /****************************************************************************/
-/*	AttachSharedInvalidationState(key)	 Attach a buffer segment			*/
+/*	AttachSharedInvalidationState(key)	 Attach to existing buffer segment	*/
 /*																			*/
-/*	should be called only by the POSTMASTER									*/
+/*	should be called by each backend during startup							*/
 /****************************************************************************/
 void
 AttachSharedInvalidationState(IPCKey key)
@@ -74,6 +63,11 @@ AttachSharedInvalidationState(IPCKey key)
 		elog(FATAL, "AttachSharedInvalidationState: failed segment init");
 }
 
+/*
+ * InitSharedInvalidationState
+ *		Initialize new backend's state info in buffer segment.
+ *		Must be called after AttachSharedInvalidationState().
+ */
 void
 InitSharedInvalidationState(void)
 {
@@ -88,24 +82,19 @@ InitSharedInvalidationState(void)
 
 /*
  * RegisterSharedInvalid
- *	Returns a new local cache invalidation state containing a new entry.
+ *	Add a shared-cache-invalidation message to the global SI message queue.
  *
  * Note:
  *	Assumes hash index is valid.
  *	Assumes item pointer is valid.
  */
-/****************************************************************************/
-/*	RegisterSharedInvalid(cacheId, hashIndex, pointer)						*/
-/*																			*/
-/*	register a message in the buffer										*/
-/*	should be called by a backend											*/
-/****************************************************************************/
 void
 RegisterSharedInvalid(int cacheId,		/* XXX */
 					  Index hashIndex,
 					  ItemPointer pointer)
 {
-	SharedInvalidData newInvalid;
+	SharedInvalidData	newInvalid;
+	bool				insertOK;
 
 	/*
 	 * This code has been hacked to accept two types of messages.  This
@@ -127,34 +116,16 @@ RegisterSharedInvalid(int cacheId,		/* XXX */
 		ItemPointerSetInvalid(&newInvalid.pointerData);
 
 	SpinAcquire(SInvalLock);
-	while (!SISetDataEntry(shmInvalBuffer, &newInvalid))
-	{
-		/* buffer full */
-		/* release a message, mark process cache states to be invalid */
-		SISetProcStateInvalid(shmInvalBuffer);
-
-		if (!SIDelDataEntries(shmInvalBuffer, 1))
-		{
-			/* inconsistent buffer state -- shd never happen */
-			SpinRelease(SInvalLock);
-			elog(FATAL, "RegisterSharedInvalid: inconsistent buffer state");
-		}
-
-		/* loop around to try write again */
-	}
+	insertOK = SIInsertDataEntry(shmInvalBuffer, &newInvalid);
 	SpinRelease(SInvalLock);
+	if (! insertOK)
+		elog(NOTICE, "RegisterSharedInvalid: SI buffer overflow");
 }
 
 /*
  * InvalidateSharedInvalid
- *	Processes all entries in a shared cache invalidation state.
+ *		Process shared-cache-invalidation messages waiting for this backend
  */
-/****************************************************************************/
-/*	InvalidateSharedInvalid(invalFunction, resetFunction)					*/
-/*																			*/
-/*	invalidate a message in the buffer	 (read and clean up)				*/
-/*	should be called by a backend											*/
-/****************************************************************************/
 void
 InvalidateSharedInvalid(void (*invalFunction) (),
 						void (*resetFunction) ())