Databases Reference
In-Depth Information
this method typically leaves larger time periods where data is lost in the event of a failure.
Transportable tablespaces and other backups from RMAN also require time to restore.
A physical standby database or RAC can offer zero data loss and faster time to recovery;
however, these solutions do require the expense of redundant hardware. Asynchronous
replication solutions also require redundant hardware, but while providing a great deal
of flexibility, also require considerable effort in planning and coding.
You should carefully balance the cost, both in extra hardware and performance, of each
of these solutions, and balance them against the potential cost of a database or server
failure. Of course, any of these solutions is infinitely more valuable than not imple‐
menting any of them and simply hoping that a disaster never happens to you.
Likely, you'll deploy combinations of these solutions such as RAC for rapid instance
recovery and Data Guard to enable business continuity during primary site failure. If
you choose to use RAC, Data Guard, or GoldenGate, you might also use
Global Data
Services
, a new configuration, maintenance, and monitoring management framework
supported by Oracle Database 12
c
, for global management of high availability config‐
urations including cloud infrastructures.
Planned Downtime
Thus far, we have focused on preventing unplanned downtime. But much of availability
planning seeks to reduce planned downtime for system maintenance operations. Plan‐
ned downtime is usually a concern during certain system changes, data changes, and
application changes. Today, much of this downtime has largely disappeared because of
Oracle's extensive online management capabilities.
For example, changes that can be made while a system is operational include hardware
upgrades, operating system upgrades, patching, and storage migration. Where RAC
configurations leverage ASM, rolling upgrades (first introduced in Oracle Database
10
g
Release 2) can take place with no downtime. In fact, Oracle's engineered systems
that run Oracle Databases are designed to take advantage of this.
Oracle Data Guard might be used to minimize downtime for system, database, and patch
set upgrades where Oracle databases are not in RAC configurations. It offers a logical
standby database capability where the standard Oracle archive logs are transformed into
SQL transactions, and these are applied to an open standby database. The logical standby
database can also be different physically from the primary database and can be used for
different tasks. For example, the primary Oracle database might be indexed for trans‐
action processing while the standby database might be indexed for data warehousing.
Although physically different from the primary database, the secondary database is
logically the same and can take over processing in case the primary fails. As archive logs
are shipped from the primary to the secondary, undo records in the shipped archive log
