Can we improve further this update query

Question

Can we optimize the following query further.
UPDATE OPTPRC_CHANGES_PK
SET UPDATEFLAG_ = 'X'
WHERE (UPDATEFLAG_ = 'U' OR UPDATEFLAG_ = 'A')
AND EXISTS
( SELECT 1 FROM OPTPRC
WHERE OPTPRC.DATE_ = OPTPRC_CHANGES_PK.DATE_
AND OPTPRC.EXCHCODE = OPTPRC_CHANGES_PK.EXCHCODE
AND OPTPRC.CONTRCODE = OPTPRC_CHANGES_PK.CONTRCODE )
The OPTPRC table contains about 10 million rows and OPTPRC_CHANGES_PK table contains about 1.5 million rows. The query takes about 20 minutes to complete. Ouch.
The index (Date_,Exchcode,contrcode) is in place on both tables.
Query Plan_
According to query plan, it is not using any indexes. Hash semi join is being used and table are fully scanned.
Oracle 10g is being used on Solaris 10.
Can we improve this query.

Answer 1

Following is th query plan for the query poposed by SeánMacGC
Query Plan
PLAN_TABLE_OUTPUT
Plan hash value: 72452462
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (
| 0 | UPDATE STATEMENT | | 1558K| 53M| | 29378
| 1 | UPDATE | OPTPRC_CHANGES_PK | | | |
|* 2 | HASH JOIN | | 1558K| 53M| 44M| 29378
|* 3 | TABLE ACCESS FULL| OPTPRC_CHANGES_PK | 1521K| 27M| | 2137
| 4 | TABLE ACCESS FULL| OPTPRC | 9968K| 161M| | 11182
Predicate Information (identified by operation id):
2 - access("OPTPRC"."DATE_"="OPTPRC_CHANGES_PK"."DATE_" AND
"OPTPRC"."EXCHCODE"="OPTPRC_CHANGES_PK"."EXCHCODE" AND
"OPTPRC"."CONTRCODE"="OPTPRC_CHANGES_PK"."CONTRCODE")
3 - filter("OPTPRC_CHANGES_PK"."UPDATEFLAG_"='A' OR
"OPTPRC_CHANGES_PK"."UPDATEFLAG_"='U')