Data Replication with SQL Remote
PART 1. Introduction to SQL Remote
CHAPTER 2. SQL Remote Replication Concepts
The following features are key to SQL Remote's design.
Support for many subscribers 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 or thousands of sales representatives from a single office database.
Transaction log-based replication SQL Remote replication is based on the transaction log. This enables it to replicate only changes to data, rather than all data, in each update. Also, log-base replication has performance advantages over other replication systems.
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.
Central administration 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.
Economical resource requirements The only software required to run SQL Remote in addition to your Adaptive Server Anywhere or Adaptive Server Enterprise DBMS is the Message Agent, and a message system. If you use the shared file link, no message system software is required as long as each remote user ID has access to the directory where the message files are stored.
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.
Multi-platform support The Message Agent for Adaptive Server Anywhere runs on Windows 95, Windows NT, Windows 3.x, NetWare, UNIX, and OS/2 platforms.
The Message Agent for Adaptive Server Enterprise runs on Windows NT, and UNIX.
The UNIX Message Agent supports only the shared file link.