Clean up some longstanding problems in shared-cache invalidation.

SI messages now include the relevant database OID, so that operations
in one database do not cause useless cache flushes in backends attached
to other databases.  Declare SI messages properly using a union, to
eliminate the former assumption that Oid is the same size as int or Index.
Rewrite the nearly-unreadable code in inval.c, and document it better.
Arrange for catcache flushes at end of command/transaction to happen before
relcache flushes do --- this avoids loading a new tuple into the catcache
while setting up new relcache entry, only to have it be flushed again
immediately.

src/backend/utils/cache/catcache.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/cache/catcache.c,v 1.79 2001/06/18 03:35:07 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/cache/catcache.c,v 1.80 2001/06/19 19:42:16 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -31,8 +31,18 @@
 
 /* #define CACHEDEBUG */		/* turns DEBUG elogs on */
 
-/* voodoo constants */
-#define NCCBUCKETS 257			/* Hash buckets per CatCache (prime!) */
+/*
+ * Constants related to size of the catcache.
+ *
+ * NCCBUCKETS should be prime and must be less than 64K (because
+ * SharedInvalCatcacheMsg crams hash indexes into a uint16 field).  In
+ * practice it should be a lot less, anyway, to avoid chewing up too much
+ * space on hash bucket headers.
+ *
+ * MAXCCTUPLES could be as small as a few hundred, if per-backend memory
+ * consumption is at a premium.
+ */
+#define NCCBUCKETS 257			/* Hash buckets per CatCache */
 #define MAXCCTUPLES 5000		/* Maximum # of tuples in all caches */
 
 
@@ -218,6 +228,11 @@ CatalogCacheInitializeCache(CatCache *cache)
 	 */
 	tupdesc = CreateTupleDescCopyConstr(RelationGetDescr(relation));
 
+	/*
+	 * get the relation's relisshared flag, too
+	 */
+	cache->cc_relisshared = RelationGetForm(relation)->relisshared;
+
 	/*
 	 * return to the caller's memory context and close the rel
 	 */
@@ -737,6 +752,7 @@ InitCatCache(int id,
 	cp->cc_relname = relname;
 	cp->cc_indname = indname;
 	cp->cc_reloidattr = reloidattr;
+	cp->cc_relisshared = false;	/* temporary */
 	cp->cc_tupdesc = (TupleDesc) NULL;
 	cp->cc_ntup = 0;
 	cp->cc_size = NCCBUCKETS;
@@ -1116,7 +1132,8 @@ ReleaseCatCache(HeapTuple tuple)
  *
  *	Note that it is irrelevant whether the given tuple is actually loaded
  *	into the catcache at the moment.  Even if it's not there now, it might
- *	be by the end of the command, so we have to be prepared to flush it.
+ *	be by the end of the command --- or might be in other backends' caches
+ * --- so we have to be prepared to flush it.
  *
  *	Also note that it's not an error if there are no catcaches for the
  *	specified relation.  inval.c doesn't know exactly which rels have
@@ -1126,7 +1143,7 @@ ReleaseCatCache(HeapTuple tuple)
 void
 PrepareToInvalidateCacheTuple(Relation relation,
 							  HeapTuple tuple,
-							  void (*function) (int, Index, ItemPointer))
+							  void (*function) (int, Index, ItemPointer, Oid))
 {
 	CatCache   *ccp;
 
@@ -1159,6 +1176,7 @@ PrepareToInvalidateCacheTuple(Relation relation,
 
 		(*function) (ccp->id,
 					 CatalogCacheComputeTupleHashIndex(ccp, tuple),
-					 &tuple->t_self);
+					 &tuple->t_self,
+					 ccp->cc_relisshared ? (Oid) 0 : MyDatabaseId);
 	}
 }