Features

Real  Application Clusters     (RAC)

Dataguard

Streams

Advance Replication

Basic Replication

Topic of Comparison

Physical  Standby

Logical   Standby

Multi-Master Replication

Updatable Materialized Views

Read-only Materialized Views

Description

Allows the Oracle database to run applications across a set of clustered servers.

Provides a physically identical copy of the primary database, with on disk database structures that are identical to the primary database on a block-for-block basis.

Contains the same logical information as the production database, although the physical organization and structure of the data can be different.

Enables information sharing in form of stream of messages. Enables the propagation and management of data, transactions, and events in a data stream.

(Also called peer-to-peer or n-way replication)  Enables multiple sites, acting as equal peers, to manage groups of replicated database objects.

Provides complete or partial copy (replica) of a target table from a single point in time. Enable users to work on a subset of a database while disconnected from the central database server.

Provides complete or partial read-only copy (replica) of a target table from a single point in time. Enable users to view a subset of a database while disconnected from the central database server.

Purpose

- High availability

- Scalability

- Redundancy during failures

- Data protection

- Disaster recovery

- High availability

- Data protection

- Disaster recovery

- Efficient use of redundant hardware

- Data distribution

- Data sharing

- Data sharing

- Data distribution

- Sharing subset of data with update access.

- Data distribution

- Sharing subset of data in read-only mode.

Hardware

All nodes must have hardware that runs same OS.

All sites must have hardware that runs same OS.

All sites must have hardware that runs same OS.

Servers with different hardware can be used.

Servers with different hardware can be used.

Servers with different hardware can be used.

Servers with different hardware can be used.

OS

Same OS on all nodes including Patchset release

Same OS. Patchset release can be different in different sites.

Same OS. Patchset release can be different in different sites.

Can be used with different OS

Can be used with different OS

Can be used with different OS

Can be used with different OS

Oracle Software

Same version on all nodes including Oracle Patchset release

Same version on all nodes including Oracle Patchset release

Same version on all nodes including Oracle Patchset release

Can be used with different Oracle versions

Can be used with different Oracle versions

Can be used with different Oracle versions

Can be used with different Oracle versions

Feature Specific Terms

Servers involved in RAC configuration are generally known as Nodes. High-speed link between nodes is called Interconnect.

Primary and Standby database servers are generally known as Primary Site and Standby Site respectively.

Primary and Standby database servers are generally known as Primary Site and Standby Site respectively.

Database from where changes are captured is called source or capture site. Database from where changes are applied is called destination or apply site.

One database where Replication Administrative activities can be performed is called Master Definition Site. All other replicated databases are called Master sites.

Database with Master table is called Master Site or Target Site. Database where Materialized view is created is called Materialized view site.

Database with Master table is called Master Site or Target Site. Database where Materialized view is created is called Materialized view site.

Database

Multiple instances linked by interconnect to share access to an Oracle database.

One production database and one or more physical standby databases.

One production database and one or more logical standby databases.

Data stream can propagate data either within a database or from one database to another.

Complete copy of replicated table is maintained in multiple databases.

Updatable Materialized view is created in database other than the one containing master table.

Read-only materialized view can be created either within a database or in another database.

Data Storage

Single database on shared storage.

Primary site and Standby sites have their own database.

Primary site and Standby sites have their own database.

Source and Destination can either be same database or they can be different databases.

All replicated master sites are having their own databases.

Master table and Materialized views are part of different databases.

Master table and Materialized views can either be in same database or they can be in different databases.

Logical Database Structure

As there is one database, there is one logical structure of the database.

As physical structure of the database is exactly (block-by-block) same, the logical structure also remains same in primary and standby databases.

When created, logical standby database has same structure as primary. Later, additional schema/objects can be created in logical standby database. However, original objects must remain same as primary.

Streams provide flexibility to have different structure of schema/objects at source and destination databases.  This can be accomplished by using transformation of messages.

Logical structure of replicated objects must be same. Owner of those objects must be same in all master sites.

Both row and column subsetting enable you to create materialized views that contain a partial copy of the data at a master table. However, they are always based on a single master table.

Both row and column subsetting enable you to create materialized views that contain a partial copy of the data at a master table. Read-only materialized views can be created using join between multiple master tables.

Architecture Overview

A cluster comprises multiple interconnected computers or servers that appear as if they are one server to end users and applications. RAC uses Oracle Clusterware for the infrastructure to bind multiple servers so that they operate as a single system. If one clustered server fails, the Oracle database will continue running on the surviving servers.

Standby database is kept synchronized with the primary database, though Redo Apply, which recovers the redo data, received from the primary database and applies the redo to the standby database. If the primary database becomes unavailable, standby database can be switched to the primary role.

Standby database is kept synchronized with the primary database though SQL Apply, which uses logminer, transforms the data from redo logs into SQL statements and then executing the SQL statements on the standby database. If the primary database becomes unavailable, standby database can be switched to the primary role.

Each unit of shared information is called a message. Streams can capture, stage, and manage messages in Queue. Messages can be DML, DDL and user-defined messages. Streams can propagate the messages from one queue to other queue. When messages reach a destination, Streams can consume them based on your specifications.

Internal triggers capture changes applied at one site. The trigger stores those captured transactions locally. The source master site pushes (propagates and applies) those transactions to destination site.

Updatable Materialized view is a view that stores view data in it's own storage. A push process that is same as multi-master replication pushes updated data from MV site. However, changes from master site are pulled by refresh site using refresh process.

Read-only Materialized view is a view that stores view data in it's own storage. Data in materialized view are refreshed by refresh process. Refresh process is initiated at Materialized view site. Refresh process pulls data from master table using SQL query that was used to create Materialized view.

Overview of Installation/Setup

RAC installation is a two-phase installation. In phase one, use Oracle Universal Installer (OUI) to install Oracle Clusterware. In second phase, use OUI to install the RAC software (I.e. Oracle RDBMS with RAC option). You must install Oracle Clusterware and Oracle RDBMS in separate home directories.

Prepare Primary Database by making required changes in parameters, logging, archiving etc. Create a Backup Copy of the Primary Database Datafiles. Create a Control File for the Standby Database. Prepare an Initialization Parameter File for the Standby Database. Copy Files from the Primary System to the Standby System. Set Up the Environment to Support the Standby Database. Start the Physical Standby Database in continuous recovery mode.

Verify prerequisites Logical Standby Database (e.g. Datatypes, Primary Key etc). Create a Physical Standby Database. Stop Redo Apply on the Physical Standby Database. Prepare the Primary Database to Support a Logical Standby Database. Convert to a Logical Standby Database. Adjust Initialization Parameters for the Logical Standby Database. Open the Logical Standby Database and then perform certain Post-Creation Steps.

Create streams administrator user in all databases. In source database, create Capture Process and Propagation schedule for propagation to destination database. Create Apply Process in destination database.  Start Supplemental Logging in source database. . Prepare source database/objects. Create copy of those objects in destination database using export/import (datapump or traditional) or using RMAN. Complete the instantiation of objects. Start Apply, Propagation and Capture processes.

Create replication administrator user at all the sites with required privileges. Create propagation from each site to all other sites. At one site create Master replication group. The group remains in quiesced state when created. This site becomes MDS. Add objects (to be replicated) in the group from MDS. Add all master sites in master group from MDS. Start replication by resuming replication group. It alters replication group from quiesced to normal state.

At master site, create replication administrator. At materialized view (MV) site, create MV administrator. Create propagation from MV site to master site. Create master group at master site and add master objects in master group. Create materialized views at MV site. Create MV group at MV site and add materialized views in the MV group. On the MV site, create refresh group and add materialized views in refresh group.  Start replication by resuming replication group.

If MV is being created in database other than the one containing master table, then create database link in MV database to point to master database for accessing master table. Create materialized view.

Database/Instance status

All or any node of RAC can have instance with database open for DML/DDL access.

Redo apply requires database in recovery mode. When Physical standby database is in recovery mode, it cannot be opened. When not in recovery mode, it can only be opened in read-only mode.

SQL Apply requires database open for running SQL statements. Hence, Logical standby database must be open in normal circumstances.

Apply process requires database open for running SQL statements. Hence, destination database must be open in normal circumstances.

Push job requires master sites to be open when it pushes transaction to other master sites. Hence, in normal circumstances, all the master databases must be open.

Push as well as refresh job requires master and MV sites to be open. Hence, in normal circumstances, the master and MV databases must be open.

Refresh job requires master and MV sites to be open. Hence, in normal circumstances, the master and MV databases must be open.

Restriction on Datatypes

As there is one database, it supports all datatypes.

As physical structure of the database is exactly (block-by-block) same, it supports all datatypes.

There is restriction on datatypes allowed in logical standby setup.

There is restriction on datatypes allowed in streams setup.

There is restriction on datatypes allowed in replicated tables.

There is restriction on datatypes allowed in materialized views.

There is restriction on datatypes allowed in materialized views.