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Data Guard Broker is
an assisting utility
provided with Oracle
Database Server
software to
facilitate the
creation and
management of data
guard
configurations. (Note:
Data
Guard Broker is
available with
Oracle 9i Release 2
or later.) Data
Guard broker
consists of server
side and client side
components
implementing a
distributed
computing
architecture. The
server side
component includes a
Data Guard Monitor (DMON)
process and
configuration files.
The client side
component includes
Data Guard Manager
and Command Line
interface.
Data Guard Broker
manages a data guard
configuration using
a broker management
model. The broker
management model is
a hierarchal
structure comprised
of Configuration,
Site and Database
resources. Broker
can manage all three
layers of the
management model. We
will see more about
the broker
management model
later in this
section.
Data Guard Broker
can manage the
primary database and
up to nine standby
databases in one
configuration. These
nine standby
databases can be a
mixture of physical
and logical standby
databases. You can
create a standby
database using Data
Guard broker, or add
an existing standby
database to a
configuration.
When you create a
standby database
using broker, broker
takes care of the
entire set of
supporting files;
e.g., SPFILE, Oracle
Net configuration
files, and so on. If
you need to add an
existing standby
database to a data
guard configuration,
you must configure
the SPFILE and
Oracle Net files
manually before
adding the standby
database to a
configuration. If
you plan to use Data
Guard Broker for the
management of
standby databases,
you must use the
persistent server
parameter file (SPFILE)
to hold the
initialization
parameters on all
the participating
databases.
Some advantages of
using Data Guard
broker are as
follows:
-
It is a
centralized
management tool
that can be used
to manage the
entire
configuration
using a GUI or
CLI interface.
-
It provides an
extensive health
check mechanism
for the primary
database,
standby
databases and
supporting
services in the
configuration.
-
It reduces the
complexity of
role management
services.
Switchover and
Failover
operations can
be performed
from a
centralized
console.
-
It can be used
to gather useful
statistics to
fine tune the
log transfer and
log apply
services.
(Note:
In Oracle 9i, Data
Guard Broker cannot
be used with Oracle
Real Application
Cluster. RAC support
is provided with
Oracle 10g.)
The following
subsections will
explain the broker
management model and
the broker
components in brief.
Configuration, Sites
and Resources
Broker management
model is a three
layer hierarchical
framework. The
logical units of the
management model are
Configuration, Site
and Database
Resources. These
three layers bear a
parent-child
relationship as
shown in the
following diagram.
Figure1: Diagram
showing relation
between layers of
Broker Management
model.
A Database resource
is the smallest unit
managed by Data
Guard Broker. In the
broker management
model, a database
resource represents
an instance of the
primary or standby
database. In
addition, a service;
e.g., log apply
service can be
classified as a
database resource in
context of a
management model.
Site in this model
is a collection of
database resources.
In other words, a
site is equivalent
to a host machine on
which a database
instance is running.
Configuration is the
largest unit in the
broker management
model consisting of
the primary site and
one or more standby
sites.
Data Guard Broker
can manage all three
layers of the
management model.
Any operation
performed on a
higher level of the
model is applicable
to all the child
objects of that
layer. For example,
if the status of a
site is changed to
offline, then all
the resources under
that site will be
offline. We will
learn more about the
management model in
Chapter 7.
Server Side
Components of the
Broker
The server side
component of Data
Guard Broker
includes the Data
Guard Monitor (DMON)
process and a
configuration file.
The Data Guard
Monitor is a
background process
that runs on each of
the sites managed by
Data Guard Broker.
The configuration
file is a binary
file that contains
the properties and
status of all the
sites in a
configuration. The
DMON process is
responsible for
managing a
consistent copy of
the configuration
file across the
entire
configuration. The
DMON processes in a
configuration
communicate over
Oracle Net to manage
the role management
and log management
services. In
addition, the DMON
process gathers
statistics about the
health of a site
that can be used for
monitoring and
fine-tuning. The
following diagram
shows a sample data
guard configuration
managed by data
guard
broker.
Figure 2: Diagram
showing server side
components of Data
Guard Broker.
Client Side
Components of the
Broker
The Data Guard
Manager and Command
Line Interface (DGMGRL)
make up the client
side components of
Data Guard Broker.
Data Guard Manager
is a graphical user
interface integrated
with Oracle
Enterprise Manager.
It contains several
wizards to ease the
management of a data
guard configuration.
DGMGRL or Command
Line Interface
provides most of the
functionalities of
Data Guard Manager
and can be very
useful to write
custom scripts to
automate data guard
tasks. Chapter 7
provides the
practical details of
data guard broker.
You will learn more
about the server
side and client side
components in that
chapter.
--
Bipul Kumar
is a Senior Oracle
Database
Administrator and
Database Architect
for an Electronic
Media Company based
in London, United
Kingdom. His
responsibilities
include Oracle
architectural
design, defining
policies and best
practices,
administering and
maintaining the
database,
supervising oracle
development and
implementing new
database
technologies. He has
more than seven
years of
experience in
creating and
managing Oracle
Databases of varying
sizes, primarily on
UNIX operating
systems.
Mr. Kumar has a
Masters degree in
Science from the
Indian Institute of
Technology (IIT),
Kharagpur, India and
nearly ten years of
experience in
computing. In
addition, he has
acquired Oracle DBA
certification for
7.3, 8.0, and 8i.
His most recent book
is
Oracle Dataguard —
Standby Database
Failover Handbook. |
