select * from ACT where STATUS='I'
Total rows in a table 508633
no of rows returned is 4
Index is there on status column .
optimizer_mode=choose

The index is not used ..Under rule based optimizer it works .
when given a hint the index is used ..

what values should I give under thses circumstance for these two parameters to make index usage ...

optimizer_index_caching 0
optimizer_index_cost_adj 100