Oracle standby reporting database

Oracle Tips

QUESTION: I want to create a cloned database that can be used for crystal reporting and standby databases. What's the best approach?

ANSWER: Oracle offers several options for creating a read-only copy of the database, each depending on your tolerance for stale data in the reporting database:

· Physical Standby Database (redo apply)

· Logical Standby Database (SQL Apply)

· Simple Replication (using snapshots)

· Streams Replication (using database, schema-level or tables level data capture)

Unless you have created a manual standby you are using Oracle data guard. Data guard is the term that defines oracle's managed standby. I think you are confusing it with Data guard Broker which is a separate configurable tool. Let's take a closer look at each approach:

Physical Standby Database

This ancient method of transporting and applying redo logs has been around for over 15 years and is very simple and reliable. Starting in 9i, the physical standby will transfer redo as it is generated, greatly reducing the chance of lossing data. The database can be queried read-only and the data will be current as of the transaction that was applied.

Physical Standby Database Downsides: The possibility of losing some transactions during a system crash.
Physical Standby Database Staleness: In 9i and 10g, redo apply must be stopped when the database is opened read only. In 11g, redo apply continues when the database is opened read only.

Logical Standby Database

The Logical Standby Database uses SQL Apply to keep a consistent replication of the primary database. The tables that are managed are also protected from modification. The main advantage of logical database is that indexes and materialized views can be added to the standby database. This is perfect for reporting application where the DBA will create pre-joined, de-normalized table structures for super-fast queries. For details, see the book "Oracle Data Guard Standby Database".

Logical Standby Database Downside: Changes made to the standby to support reporting can case performance problems it the standby is activated.
Logical Standby Database Staleness: Same as the Physical Standby except that the standby is always open.

Simple Replication

Oracle offers simple (snapshot) replication whereby mview logs are created for all replicated tables, and the logs are used to update the tables on the standby database at specified intervals (from "on commit" to any delayed time period). For details, see the book "Oracle Replication".

Simple Replication Downside: No managed switchover/failover however both databases are open and available.
Simple Replication Staleness: User-defined, from "On commit" to a defined refresh interval.

Streams Replication

Oracle Streams is a great solution and Streams provides high-speed data replication with a minimum of set-up fuss. Using database, schema or table level data capture it is easy to define a replication strategy. Both databases are open read-write. There is no protection such as on the Logical Standby. For more details, see the book "Oracle Streams" and its handy code depot.

Streams Replication Database Downside: No managed switchover/failover but both databases open and available.
Simple Replication Database Staleness: Normally negligible.

��