Data Distributor  Concept

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Data Distributor uses the same replication model as Microsoft® SQL Server™ replication model that is based on the “publish and subscribe” metaphor. The replication model consists of Publishers, Distributors, and Subscribers, articles and publications, and push and pull subscriptions.

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 Replication Model
 Push Subscriptions
 Pull Subscriptions

Configuring a replication system is made easier with replication wizards, available from the Data Distributor Manager. You can use these wizards to enable, modify, and disable IBM AS/400, Microsoft SQL, Oracle and Open/36 servers as Publishers.

You can use the Data Distributor Create Publication Wizard and the Push Subscription Wizard to easily define your publications and the subscriptions.

You can decide if the publications will be published via the SQL Distribution Server or directly to the subscriber(s) by Data Distributor. Depending on your data distribution needs, you can use one or both replication methods. For more information on those replication methods, see Replication Methods.

You can also use the Push Subscription Wizard and the Pull Subscription Wizard available from the SQL Server Enterprise Manager to manage subscriptions to publications created by Data Distributor.

You can use the Replication Monitor available from the SQL Server Enterprise Manager to monitor replication activities for publications published via the SQL Distribution Server.

You can use the Data Distributor's Replication Monitor to monitor replication activities for publications published directly to the subscriber(s) by Data Distributor.


The Replication Model

The following will describe the various terms and concepts that Data Distributor inherited from replication model introduced by the Microsoft® SQL Server™.

A Publisher is an IBM AS/400, MS SQL, Oracle or Open/36 server that makes data available for replication to other servers. In addition to identifying which data is to be replicated, the publisher detects which data has changed and maintains information about all publications at that site. Any given data element that is replicated has a single publisher, even if it may be updated by any number of subscribers or published again by a subscriber.

Subscribers are SQL Servers, Local or Network computers, Internet Locations or other types of subscribers, servers or applications such as IBM AS/400 servers, Oracle servers, Open/36 servers, MS Access and MS Excel that are supported by the Data Distributor replication methods. Subscribers are servers that store replicas and receive updates.

A Publication is simply a collection of articles, and an article is a grouping of data to be replicated. An article can be an entire file, table or view, only certain fields or columns (using a vertical filter) or only certain records or rows (using a horizontal filter).

A publication often has multiple articles. This grouping of multiple articles makes it simpler to subscribe to a unit (the publication), which has all the relevant and required data. Subscribers subscribe only to a publication, not to individual articles within a publication.


Push Subscriptions

With a Push Subscription, the publisher (IBM AS/400, MS SQL, Oracle or Open/36 server) propagates the changes to a subscriber without a request from the subscriber to do so. Typically, push subscriptions are used in applications that are required to send changes to subscribers whenever and as soon as they occur. Push subscriptions are best for publications that require near-real-time movement of data without polling and where the higher processor overhead at the publisher does not affect performance. Changes can also be pushed to subscribers on a scheduled basis.


Pull Subscriptions

With a Pull Subscription, the subscriber asks for periodic updates of all changes at the publisher. Pull subscriptions are best for publications having a large number of subscribers (for example, subscribers using the Internet). Pull subscriptions are also best for autonomous mobile users because they allow the user to determine when the data changes are synchronized. A single publication can support a mixture of push and pull subscriptions. Pull Subscriptions are initiated outside of Data Distributor. Refer to Microsoft® SQL Server™ Books On-Line for more information on Pull Subscriptions.