Recently, we configured Oracle 10g Release2 RAC with two nodes on Red hat Linux (64 bit). Then we created users and imported data from our production (single instance, Oracle 10g Release2 on Red hat Linux 64 bit) database server. When the reports are opening from new RAC server, we observed that it is taking more time when compared to single instance database. For one particular report, the report is taking 1 minute 40 sec in single instance database server, but the same report taking 5 min 30 sec in RAC environment.

When I checked in v$sqlarea, in RAC environment, the sql statement is taking more CPU time (101 sec) and Buffer gets(77220000) as compared to 5 sec of CPU time and 4700000 of buffer_gets in single instance database. I checked the execution plan. RAC is using a different execution plan, but the "COST" of RAC execution plan is 336 as compared to 1600 of single instance database

I am not able to understand, when the execution plan of RAC is better than that of single instance database server, why RAC is taking more CPU time and why RAC is fetching more buffer.

Any help is greatly appreciated.