Manage Subscriptions

Subscriptions resemble SQL select statements. They identify the replication definition or publication to which you are subscribing, the source and destination databases and data servers, and the materialization method by which the initial information is to be copied.

You can use a where clause to specify a subset of rows or parameters that the destination database receives from the source database.

Materialization is the process of copying data specified by a subscription from a primary database to a replicate database, thereby initializing the replicate table. Replicate data can be transferred over a network, or, for subscriptions involving large amounts of data, loaded initially from media. Initialization from media is called bulk materialization. You use one of four materialization methods, depending on how you want materialization to affect the replication system.

Subscriptions for database replication definitions instruct Replication Server to replicate database objects from the primary to the replicate database. You can choose to replicate or not replicate individual tables, transactions, functions, system stored procedures, and data definition language (DDL). This method, called multisite availability (MSA), requires only a single database replication definition for each primary database and a single subscription for each subscribing database.

Subscriptions for table replication definitions instruct Replication Server to replicate data from primary tables into specified replicate tables. After you have created a replication definition for a primary table, replicate sites must subscribe to the replication definition at the primary database to receive updates.

Subscriptions for function replication definitions require you to use the no-materialization or the bulk materialization methods.

You can subscribe to a group of replication definition articles by subscribing to a publication. Publication subscriptions cannot contain where clauses. To subscribe to a subset of rows in an article, you must include a where clause when you create the article.

You create subscriptions at the Replication Server managing the database where the replicate data is to be maintained. Your previously created replication definition provides the location of the primary data and defines the structure of the primary table and optionally, of the replicate table, where they differ.

Subscriptions are added to the rs_subscriptions system table for both the primary and the replicate Replication Server. The materialization method you select determines how you create subscriptions.

Because a subscription can replicate a large set of rows, materialization can burden the network or impede applications that use the primary or replicate data.

• Subscription Materialization Methods
  Replication Server offers four methods for creating subscriptions, so you can regulate the effects of materialization on the replication system.
• Dematerialization Processing
  Dematerialization removes subscriptions and, optionally, data from the replicate database. Dematerialization also removes subscription information from the RSSDs at the primary and replicate sites.
• Monitor Materialization and Dematerialization
  Subscriptions pass through phases before they are fully set up or removed from the replication system. Learn the phases for setting up a subscription or removing subscription data.
• Verifying that the Replication System Is Ready Before You Create Subscriptions
  Before creating subscriptions, verify that the replication system is ready.
• Subscription Commands
  Learn how to manage subscriptions with RCL commands.
• Subscription Example
  The subscription example shows you how to use RCL commands to replicate the publishers table from a primary Adaptive Server database to a replicate Adaptive Server database by creating an atomic subscription to the table replication definition. You can also do this in Sybase Central.
• Materialize text, unitext, image, and rawobject Data
  In general, you can use any materialization method for subscriptions for tables with columns that use the text, unitext, image, or rawobject datatypes.
• Subscriptions for Columns with Heterogeneous Datatypes
  You create subscriptions for table replication definitions in the normal manner when class-level or column-level translations are defined and active. However, certain restrictions apply to use of the where clause.
• Bitmap Subscriptions
  Bitmap subscriptions allow you to create subscriptions that replicate rows based on bitmap comparisons.
• Obtain Subscription Information
  Once data is replicating, you may need to obtain information about the subscriptions or verify that data is replicating consistently. Replication Server provides stored procedures for obtaining information and a standalone utility for verifying consistency.
• Publication Subscriptions
  With publication subscriptions, you create subscriptions for a group of replication definitions using a single command.