Revise hash join and hash aggregation code to use the same datatype-

specific hash functions used by hash indexes, rather than the old
not-datatype-aware ComputeHashFunc routine.  This makes it safe to do
hash joining on several datatypes that previously couldn't use hashing.
The sets of datatypes that are hash indexable and hash joinable are now
exactly the same, whereas before each had some that weren't in the other.

src/backend/utils/cache/lsyscache.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/cache/lsyscache.c,v 1.95 2003/05/26 00:11:27 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/cache/lsyscache.c,v 1.96 2003/06/22 22:04:54 tgl Exp $
  *
  * NOTES
  *	  Eventually, the index information should go through here, too.
@@ -16,8 +16,10 @@
 #include "postgres.h"
 #include "miscadmin.h"
 
+#include "access/hash.h"
 #include "access/tupmacs.h"
 #include "catalog/pg_amop.h"
+#include "catalog/pg_amproc.h"
 #include "catalog/pg_namespace.h"
 #include "catalog/pg_opclass.h"
 #include "catalog/pg_operator.h"
@@ -28,6 +30,7 @@
 #include "nodes/makefuncs.h"
 #include "utils/array.h"
 #include "utils/builtins.h"
+#include "utils/catcache.h"
 #include "utils/datum.h"
 #include "utils/lsyscache.h"
 #include "utils/syscache.h"
@@ -106,6 +109,72 @@ get_opclass_member(Oid opclass, int16 strategy)
 	return result;
 }
 
+/*
+ * get_op_hash_function
+ *		Get the OID of the datatype-specific hash function associated with
+ *		a hashable equality operator.
+ *
+ * Returns InvalidOid if no hash function can be found.  (This indicates
+ * that the operator should not have been marked oprcanhash.)
+ */
+Oid
+get_op_hash_function(Oid opno)
+{
+	CatCList   *catlist;
+	int			i;
+	HeapTuple	tuple;
+	Oid			opclass = InvalidOid;
+
+	/*
+	 * Search pg_amop to see if the target operator is registered as the "="
+	 * operator of any hash opclass.  If the operator is registered in
+	 * multiple opclasses, assume we can use the associated hash function
+	 * from any one.
+	 */
+	catlist = SearchSysCacheList(AMOPOPID, 1,
+								 ObjectIdGetDatum(opno),
+								 0, 0, 0);
+
+	for (i = 0; i < catlist->n_members; i++)
+	{
+		Form_pg_amop aform;
+
+		tuple = &catlist->members[i]->tuple;
+		aform = (Form_pg_amop) GETSTRUCT(tuple);
+
+		if (aform->amopstrategy == HTEqualStrategyNumber &&
+			opclass_is_hash(aform->amopclaid))
+		{
+			opclass = aform->amopclaid;
+			break;
+		}
+	}
+
+	ReleaseSysCacheList(catlist);
+
+	if (OidIsValid(opclass))
+	{
+		/* Found a suitable opclass, get its hash support function */
+		tuple = SearchSysCache(AMPROCNUM,
+							   ObjectIdGetDatum(opclass),
+							   Int16GetDatum(HASHPROC),
+							   0, 0);
+		if (HeapTupleIsValid(tuple))
+		{
+			Form_pg_amproc aform = (Form_pg_amproc) GETSTRUCT(tuple);
+			RegProcedure result;
+
+			result = aform->amproc;
+			ReleaseSysCache(tuple);
+			Assert(RegProcedureIsValid(result));
+			return result;
+		}
+	}
+
+	/* Didn't find a match... */
+	return InvalidOid;
+}
+
 
 /*				---------- ATTRIBUTE CACHES ----------					 */
 
@@ -284,6 +353,31 @@ opclass_is_btree(Oid opclass)
 	return result;
 }
 
+/*
+ * opclass_is_hash
+ *
+ *		Returns TRUE iff the specified opclass is associated with the
+ *		hash index access method.
+ */
+bool
+opclass_is_hash(Oid opclass)
+{
+	HeapTuple	tp;
+	Form_pg_opclass cla_tup;
+	bool		result;
+
+	tp = SearchSysCache(CLAOID,
+						ObjectIdGetDatum(opclass),
+						0, 0, 0);
+	if (!HeapTupleIsValid(tp))
+		elog(ERROR, "cache lookup failed for opclass %u", opclass);
+	cla_tup = (Form_pg_opclass) GETSTRUCT(tp);
+
+	result = (cla_tup->opcamid == HASH_AM_OID);
+	ReleaseSysCache(tp);
+	return result;
+}
+
 /*				---------- OPERATOR CACHE ----------					 */
 
 /*