|
Sys Admin and The Perl
Journal CD-ROM version 12.0
Version 12.0 delivers every issue of Sys Admin from 1992 through 2006 and every
issue of The Perl Journal from 1996-2002 in one convenient CD-ROM!
Order now! |
|
 |
|
|
Sidebar: Should I Use Archiving?
In one word, yes! Having logs available during a recovery
is a
tremendous help. There are several things that you can
do with logs that
simply are not possible without them:
Restore up to the point of failure. Otherwise, you
will only be able
to restore up to your last good backup. That means if
a failure occurred
at 4 p.m., you would lose an entire day's work.
Restore to the point just before the failure. If the
failure was
caused by human error (delete table), you can restore
the database to
the way it appeared just before the error.
Restore the database using an old backup. If you have
logs, it does
not matter if last night's backup failed. You can use
a backup that is
days old, or even weeks old, and restore up to the last
redo log.
Restore only the damaged disk or files. Without redo
logs, if you have
a 60 Gb database, and lose one 2 Gb disk, you must restore
the entire 60
Gb. With redo logs, you only have to restore that disk.
You can then use
redo logs to sync the restored files with the undamaged
files. This
feature of archiving saves hours in a typical restore.
Hot backups are not possible if archiving is not enabled.
There are two common arguments for not using archiving.
The first is
that it would decrease performance. The performance
loss is relatively
minor, unless you have some parameters set incorrectly.
It is important
to know that redo logs are always being created in every
Oracle
instance. Enabling archiving simply copies the closed
redo log to
another directory for recovery purposes. Before you
make any decision
about archiving, you should benchmark your instance
with and without
archiving. (A recent benchmark I performed showed a
2.5 percent
performance loss during continuous loads.)
|
|
|
|
