Informix Guide to SQL: Tutorial

Informix Guide to SQL: Tutorial
Chapter 4: Modifying Data

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Data Replication

Data replication, in the broadest sense of the term, is when database objects have more than one representation at more than one distinct site. For example, one way to replicate data, so that reports can be run against the data without disturbing client applications that are using the original database, is to copy the database to a database server on a different computer.

The following list describes the advantages of data replication:

Clients accessing replicated data locally, as opposed to remote data that is not replicated, experience improved performance because they do not have to use network services.
Clients at all sites experience improved availability with replicated data, because if local replicated data is unavailable, a copy of the data is still available, albeit remotely.

These advantages do not come without a cost. Data replication obviously requires more storage for replicated data than for unreplicated data, and updating replicated data can take more processing time than updating a single object.

Data replication can actually be implemented in the logic of client applications, by explicitly specifying where data should be found or updated. However, this way of achieving data replication is costly, error-prone, and difficult to maintain. Instead, the concept of data replication is often coupled with replication transparency. Replication transparency is functionality built into a database server (instead of client applications) to handle the details of locating and maintaining data replicas automatically.

INFORMIX-Universal Server Data Replication

Within the broad framework of data replication, Universal Server implements nearly transparent data replication of entire database servers. All the data managed by one Universal Server is replicated and dynamically updated on another Universal Server, usually at a remote site. Universal Server data replication is sometimes called hot site backup, because it provides a means of maintaining a backup copy of the entire database server that can be used quickly in the event of a catastrophic failure.

Because Universal Server provides replication transparency, you generally do not need to be concerned with or aware of data replication; the Universal Server administrator takes care of it. However, if your organization decides to use data replication, you should be aware that special connectivity considerations exist for client applications in a data replication environment. These considerations are described in the INFORMIX-Universal Server Administrator's Guide.

Informix Guide to SQL: Tutorial, version 9.1
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