Hi Tom,

I need some advices on correct bitmap selection.

We have a table with 200,000,000 Records of some payment cards transactions. Each transaction has a unique CardSerialNumber and a TransactionCounter which is generated by the card itself, so we would like to have no duplicate CardSN+TransCounter in the table.
We have 2,000,000 Cards so the Count(distinct CardSN) <= 2,000,000
And counter is 1,2,3,...

So My Question:
1- Which one is better: Either Unique BTree index on both fields or Unique Bitmap Index on them?
2- Does a Bitmap Index on the table and a unique constraint working together ?
3- Is this method more suitable: Allow to insert duplicate rows, and delete them at the end of day?

Thank you

create table t (
  c1 int unique, 
  c2 int
);

create bitmap index i2 on t(c2);

alter table t add constraint u unique (c2) using index i2;

ORA-14196: Specified index cannot be used to enforce the constraint.