ORA-01555: Snapshot too old

Solution :

1. Try to run long running queries on off peak hours, when there is less DML transactions on database.
2. Database should be in Automatic Undo Management mode.
3. Use a large optimal size of rollback segment (undo) size.
4. Use a large optimal value for undo_retention.
5. Should avoid to fetch (select / cursors) between commits.
6. Should Commit less often at the time of long running query, to reduce Undo Segment reuse.