User's Guide Part III. Using SQL Anywhere Chapter 27. Introduction to SQL Remote ReplicationThe following features are key to SQL Remote's design.
SQL Remote replication is based on the transaction log, enabling it to replicate only changes to data, rather than all data, in each update.
The transaction log is the repository of all changes made to a database. SQL Remote replicates changes made to databases as recorded in the transaction log. Periodically, all committed transactions in the consolidated database transaction log belonging to any publication are sent to remote databases. At remote sites, all committed transactions in the transaction log are periodically submitted to the consolidated database.
By replicating only committed transactions, SQL Remote ensures proper transaction atomicity throughout the replication setup and maintains a consistency among the databases involved in the replication, albeit with some time lag while the data is replicated.
SQL Remote is designed to be centrally administered, at the consolidated database. This is particularly important for mobile workforce applications, where laptop users should not have to carry out database administration tasks. It is also important in replication involving small offices that have servers but little in the way of administration resources.
Administration tasks include setting up and maintaining publications, remote users, and subscriptions, as well as correcting errors and conflicts if they occur.
For information on administering remote users, see "Granting and revoking REMOTE and CONSOLIDATE permissions".
For information on administering publications, see "Setting up publications".
For information on administering subscriptions, see "Setting up subscriptions".
For information on replication conflicts and their management, see "Error reporting and conflict resolution in SQL Remote".
The passthrough mode is designed for direct intervention at remote databases from the consolidated site, and is described in "Using passthrough mode for administration".
You can carry out many administration tasks from the Sybase Central database management tool.
SQL Remote is designed to support replication with many subscribers to a publication.
This feature is of particular importance for mobile workforce applications, which may require replication to the laptop computers of hundreds of sales representatives from a single office database.
The only software required to run SQL Remote in addition to the SQL Anywhere engine is the Message Agent, which is an executable named DBREMOTE, and a message system. If you use the shared file link, no message system software is required as long as you have access to the directory where the message files are stored.
The Message Agent runs on Windows, DOS, Windows NT, and OS/2 platforms. The DOS Message Agent supports only the shared file link. Any SQL Anywhere server or standalone engine can act as a consolidated or remote database.
Memory and disk space requirements have been kept moderate for all components of the replication system, so that you do not have to invest in extra hardware to run SQL Remote.