Recovery Manager Restore and Recovery Techniques - Oracle 10g/11g Data and Database Management Utilities - page 144

In the following scenario there were several transactions applied against the
database. After the commit is confirmed, all the changes are recorded at the
CURRENT redo log group. The CURRENT redo log group is lost. At this point
an incomplete recovery takes place. There may still be transactional activity at the
database, but sooner or later all the transactional activity will be frozen.
Once the database is not able to handle any more transactions all transactional
activity will be stuck until the situation that prevents the redo entries from being
stored in the redo log files is corrected. In the meantime all attempts to login to the
database will be greeted with this error message:
[oracle@alpha ~]$ sqlplus scott/tiger
SQL*Plus: Release 10.2.0.4.0 - Production on Fri Jun 5 23:48:09 2009
Copyright (c) 1982, 2007, Oracle. All Rights Reserved.
ERROR:
ORA-00257: archiver error. Connect internal only, until freed.
Enter user-name:
At this point the first reaction the DBA may have is to shut down the
instance. In this kind of scenario this will lead to a definite loss of data.
In the following scenario the CURRENT redo log file is lost after a high
transactional activity.