All typical database files can be created
using ASM, except for administrative files, including trace files, alert logs, backup files, export
files, and core dump files.
OMF is a handy option when you want to let Oracle manage the datafile naming for you,
whether the datafile is on a conventional file system or in an ASM disk group. You can also mix
and match: some of your datafiles can be OMF-named, and others manually named.
Undo Management Considerations
Creating an undo tablespace provides a number of benefits for both the DBA and a typical database
user. For the DBA, the management of rollback segments is a thing of the past??”all undo segments
are managed automatically by Oracle in the undo tablespace. In addition to providing a readconsistent
view of database objects to database readers when a long transaction against an object is
in progress, an undo tablespace can provide a mechanism for a user to recover rows from a table.
A big enough undo tablespace will minimize the possibility of getting the classic ???Snapshot
too old??? error message, but how much undo space is enough? If it is undersized, then the
availability window for flashback queries is short; if it is sized too big, disk space is wasted and
backup operations may take longer than necessary.
A number of initialization parameter files control the allocation and use of undo tablespaces.
The UNDO_MANAGEMENT parameter specifies whether AUTOMATIC undo management is used,
and the UNDO_TABLESPACE parameter specifies the undo tablespace itself.
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