Optimizing the query - which takes more time

Question

Hi,
Am having a query which was returning the results pretty fast one week back but now the same query takes more time to respond, nothing much changed in the table data, what could be the problem. Am using IN in the where clause, whether that could be an issue? if so what is the best method of rewriting the query.
SELECT  RI.RESOURCE_NAME,TR.MSISDN,MAX(TR.ADDRESS1_GOOGLE) KEEP(DENSE_RANK LAST ORDER BY TR.MSG_DATE_INFO) ADDRESS1_GOOGLE,
                MAX(TR.TIME_STAMP) MSG_DATE_INFO FROM  TRACKING_REPORT TR, RESOURCE_INFO RI
                WHERE TR.MSISDN IN ( SELECT  MSISDN FROM  RESOURCE_INFO WHERE GROUP_ID ='4'
               AND COM_ID='12') AND RI.MSISDN = TR.MSISDN
               GROUP BY  RI.RESOURCE_NAME,TR.MSISDN ORDER BY MSG_DATE_INFO DESC

Answer 1

Hi
i have followed this link http://www.lorentzcenter.nl/awcourse/oracle/server.920/a96533/sqltrace.htm in enabling the trace and found out the following trace output, can you explain the problem here and its remedial action pls.
SELECT  RI.RESOURCE_NAME,TR.MSISDN,MAX(TR.ADDRESS1_GOOGLE) KEEP(DENSE_RANK
  LAST ORDER BY TR.MSG_DATE_INFO) ADDRESS1_GOOGLE,                      MAX(TR.TIME_STAMP)
  MSG_DATE_INFO
FROM
  TRACKING_REPORT TR, RESOURCE_INFO RI                          WHERE RI.GROUP_ID ='426'                         AND
  RI.COM_ID='122' AND RI.MSISDN = TR.MSISDN                      GROUP BY  RI.RESOURCE_NAME,
  TR.MSISDN
call     count       cpu    elapsed       disk      query    current        rows
Parse        1      0.01       0.02          0          0          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch        6     13.69     389.03      81747     280722          0          72
total        8     13.70     389.05      81747     280722          0          72
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 281 
Rows     Row Source Operation
     72  SORT GROUP BY
276558   NESTED LOOPS 
     79    TABLE ACCESS FULL RESOURCE_INFO
276558    TABLE ACCESS BY INDEX ROWID TRACKING_REPORT
276558     INDEX RANGE SCAN TR_INDX_ON_MSISDN_TIME (object id 60507)
********************************************************************************and the plan_table output is
STATEMENT_ID     TIMESTAMP     REMARKS     OPERATION     OPTIONS     OBJECT_NODE     OBJECT_OWNER     OBJECT_NAME     OBJECT_INSTANCE     OBJECT_TYPE     OPTIMIZER     SEARCH_COLUMNS     ID     PARENT_ID     POSITION     COST     CARDINALITY     BYTES     OTHER_TAG     PARTITION_START     PARTITION_STOP     PARTITION_ID     OTHER     DISTRIBUTION     CPU_COST     IO_COST     TEMP_SPACE     ACCESS_PREDICATES     FILTER_PREDICATES
     23-Mar-11 23:36:45          SELECT STATEMENT                                   CHOOSE          0          115     115     1058     111090                                        115               
     23-Mar-11 23:36:45          SORT     GROUP BY                                        1     0     1     115     1058     111090                                        115               
     23-Mar-11 23:36:45          NESTED LOOPS                                             2     1     1     9     4603     483315                                        9               
     23-Mar-11 23:36:45          TABLE ACCESS     FULL          BSNL_RTMS     RESOURCE_INFO     2          ANALYZED          3     2     1     8     1     30                                        8               "RI"."GROUP_ID"=426 AND "RI"."COM_ID"='122'
     23-Mar-11 23:36:45          TABLE ACCESS     BY INDEX ROWID          BSNL_RTMS     TRACKING_REPORT     1          ANALYZED          4     2     2     1     3293     246975                                        1               
     23-Mar-11 23:36:45          INDEX     RANGE SCAN          BSNL_RTMS     TR_INDX_ON_MSISDN_TIME          NON-UNIQUE          1     5     4     1     1     3293                                             1          "RI"."MSISDN"="TR"."MSISDN"