ORA-01555: snapshot too old: rollback segment number with name “***” too small

Background

When I export data from oracle database, I encountered
error “ORA-01555: snapshot too old: rollback segment number
with name “***” too small”

Soluton

Check undo retention period
you can see the default value is 900 seconds(15 minutes)

SQL>show parameter undo_retention;
NAME TYPE VALUE
undo_retention integer 900

Modify undo_retention to 10800 seconds(3 hours)

SQL>ALTER SYSTEM SET undo_retention=10800 SCOPE=BOTH;

Confirm undo retention period

SQL>show parameter undo_retention;
NAME TYPE VALUE
undo_retention integer 10800

Conclusion

I exported database again, this error was disapeared.