Performance problems with Oracle 9.2.0.2 Database with optimizer_mode=RULE

Question

If I make an explain plan for a query of the following form:
SELECT a.*
FROM a, b
WHERE a.pk = b.fk
AND b.pk IN (1, 2);
the explain plan states, that a FULL-TABLE-SCAN on table b is performed and a HASH-JOIN is done to execute the query.
On 8.0.6 Database the Indexes on the tables are used and a NESTED-LOOP join is performed.
Why is the 9.2.0.2 Database using HASH-JOINS when the Database is explicitly set to optimizer_mode=RULE, as I think HASH-JOINS are only possible with CBO?
How can I force the 9.2.0.2 database to perform exactly like the 8.0.6 database with RBO?

Answer 1

some options:
set the hash_join_enabled parameter to false in the init.ora file.
set the compatible parameter to 8.0 in the init.ora file.
documentation:
HASH_JOIN_ENABLED specifies whether the optimizer should consider using a
hash join as a join method. When set to FALSE, hash join is turned off; that is, it is
not available as a join method that the optimizer can consider choosing. When set to
TRUE, the optimizer will compare the cost of a hash join to other types of joins, and
choose it if it gives the best cost.
COMPATIBLE allows you to use a new release, while at the same time guaranteeing
backward compatibility with an earlier release. This is in case it becomes necessary
to revert to the earlier release. This parameter specifies the release with which the
Oracle server must maintain compatibility. Some features of the current release may
be restricted.