Function Based Index

Hello everybody,
I have a function based index but the CBO is not using it. The DML that I
expect to have a plan with index range scan is doing a FTS. Its a simple
DML that deletes 1000 rows at a time in a loop and is based on the column
on which the FBI is created. The DML is executed as a part of a batch job
at eod.

'Explain plan for' for the DML with the same values, shows an index range
scan as expected. hence 10053 would also show the same, I guess.

This is 10205 on solaris x86 and optimizer statistics are gathered for the
table, index and the virtual/hidden column.

How do I find out why is the CBO not using the FBI.

Surprisingly, neither AWR nor statspack report show the DML which should
have appeared because another DML that has a much lesser elapsed time or
has comparatively less number of executions appears in the report.
Yesterday I enabled a 10046 trace and then confirmed via tkprof that it is
indeed doing a FTS and not index range scan.

Thanks.


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