Oracle does not recommend using the HASH_AREA_SIZE parameter unless the instance is configured with the shared server option. Oracle recommends that you enable automatic sizing of SQL working areas by setting PGA_AGGREGATE_TARGET instead. HASH_AREA_SIZE is retained for backward compatibility.
HASH_AREA_SIZE is relevant to parallel execution operations and to the query portion of DML or DDL statements. It specifies the maximum amount of memory, in bytes, to be used for hash joins.