Oracle Error: ORA-01555: snapshot too old

The errors are:

• The following error is displayed in the user interface.

  error in processing SQL query

• The following error occurs in the log file.

  (PID=14539) Database error (5): [SERVERERROR] Error from Server: ORA-01555: snapshot too old: rollback segment number 1 with name "R02" too small DB vendor code: 1555

Solution: The rollback segment keeps undo information for the transaction. This is needed for read consistency. A Select statement does not cause a rollback to be held. As soon as the transaction that generated the rollback commits, that rollback may be overwritten by another query. With a long-running Select query, the earlier rollback segments may be overwritten to the extent that the Oracle database cannot produce a result consistent with the start of the query.

If this error occurs often, a database administrator should add more rollback segments, or make existing ones larger.