Creating a subscription defines the data to be received. It does not synchronize a subscription (provide an initial copy of the data) or start (exchange messages) a subscription.
Synchronizing a subscription causes the Message Agent to send a copy of all rows in the subscription to the subscriber. It assumes that an appropriate database schema is in place. Subscriptions are synchronized using the SYNCHRONIZE SUBSCRIPTION statement.
When synchronization messages are received at a subscriber database, the Message Agent replaces the current contents of the database with the new copy. Any data at the subscriber that is part of the subscription, and which has not been replicated to the consolidated database, is lost. Once synchronization is complete, the subscription is started by the Message Agent using the START SUBSCRIPTION statement.
Synchronizing databases over a message system may lead to large volumes of messages. In many cases, it is preferable to use the extraction process to synchronize a database locally without placing this burden on the message system.
If a remote database becomes out of step with the consolidated database, and cannot be brought back in step using the SQL passthrough capabilities of SQL Remote, synchronizing the subscription forces the remote database into step with the consolidated database by copying the rows of the subscription from the consolidated database over the contents at the remote database.
Any data in the remote database that is part of the subscription, but which has not been replicated to the consolidated database, is lost when the subscription is synchronized. You may want to unload or back up the remote database using Sybase Central or, for SQL Anywhere, the dbunload utility before synchronizing the database.
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