Disable archive log mode – np. przed Importem
Shutdown edit pfile / spfile (spfile when instance is up of course) to say log_archive_start = false.
startup mount
alter database noarchivelog;
alter database open;
Remember that once you disable archive log mode you need to take a fresh backup once archive log mode is turned back on.
Object Already Exists
If a database object to be imported already exists in the database, an object creation error occurs. What happens next depends on the setting of the IGNORE parameter.
If IGNORE=n (the default), the error is reported, and Import continues with the next database object. The current database object is not replaced. For tables, this behavior means that rows contained in the export file are not imported.
If IGNORE=y, object creation errors are not reported. The database object is not replaced. If the object is a table, rows are imported into it. Note that only object creation errors are ignored; all other errors (such as operating system, database, and SQL errors) are reported and processing may stop.
Caution:
Specifying IGNORE=y can cause duplicate rows to be entered into a table unless one or more columns of the table are specified with the UNIQUE integrity constraint. This could occur, for example, if Import were run twice.
COMMIT
Default: n
Specifies whether Import should commit after each array insert. By default, Import commits only after loading each table, and Import performs a rollback when an error occurs, before continuing with the next object.
CONSTRAINTS
Default: y
Specifies whether or not table constraints are to be imported. The default is to import constraints. If you do not want constraints to be imported, you must set the parameter value to n.
Note that primary key constraints for index-organized tables (IOTs) and object tables are always imported.
Źródła:
http://download.oracle.com/docs/cd/B10500_01/server.920/a96652/ch02.htm
http://www.dba-oracle.com/bk_disable_archive_log_mode.htm