Backup and Recovery Features
Oracle offers new backup and recovery
features. You can now archive to multiple archivelog destinations.
New features in Oracle standby databases make it much easier to
administer. Oracle introduced log miner, a tool that allows you to
mine the database redo logs for all sorts of information.
RMAN is just better in 8i. Most recovery catalog
requirements are gone. The duplicate command is new in 8i.
Tablespace point in time recovery is now supported and new views
help you monitor performance of RMAN (v$backup_sync_io and
Multiplexed Archived Redo Logs
Oracle now allows you to multiplex archived
redo log locations to up to 5 different locations. This is done with
the new log_archive_dest_n parameter. You can also define the
state of those locations with the log_archive_dest_state_n
parameter to enable or defer archiving to a defined location.
Standby database in Oracle now allows for
managed recovery mode. When the standby database is put in this
mode, it will apply redo from the primary database automatically
with no administrator interaction (or scripts) required. Note that
this mode is mutually exclusive with the standby database when it’s
open in read-only mode (another new feature!). To put the database
in managed recovery mode issue the following command:
recover managed standby database;
If you want to open your standby database in
read-only mode, issue the following command:
Alter database open read only;
When you are done, you can simply shutdown the
instance and then re-mount it to start managed recovery again.
Perhaps one of the most underutilized Oracle
utilities, logMiner was released in Oracle version 8i. This utility
reads the online and archived redo log file and populates views that
the Remote DBA can query to analyze the redo stream. With this utility you
can see most database changes, who made them and when. The
dbms_logmnr and dbms_logmnr_d packages are available in
8i to manage log miner operations and create the log miner
dictionary file. A new view, V$LOGMNR_CONTENTS is available to query
the results of your log mining session.
Oracle8i introduced Materialized views that
allow you to denormalize database structures in a much easier way
than was possible in the past. This allows you to provide calculated
summary views of data in your database. Unfortunately, there are a
number of restrictions with fast refresh and multi-table joins that
make this new feature somewhat difficult to work with.
Query rewrite is another feature related to
materialized views. With Query rewrite Oracle can look at a SQL
query, and given the correct conditions, rewrite that query to make
use of an existing materialized view. This can improve the
performance of that query.
Note: Oracle also renames snapshot
replication objects to materialized views.
Note: It is a common misconception that local
materialized views can not be fast refreshed if they involve a join.
This is not the case.