Replication System Components

The basic components of a replication system are the primary database, the replicate database, and Replication Server.

Typical Sybase Replication System
A typical replication system consists of a primary database, a Replication Agent instance, one or more Replication Server intances, and a replicate database.

A typical replication system consists of a primary database, a Replication Agent instance, one or more Replication Server intances, and a replicate database.

Primary Databases

A primary database is the source of transactions that modify data in the replicate databases. Transactions are replicated by table or by procedure.

Tables marked for replication in a primary database are called primary tables. A primary table must be marked for replication so that the Replication Agent can identify and replicate the transactions that affect the data in that table. By default, Large-object (LOB) columns within a primary table are marked for replication.

To replicate invocations of a stored procedure, the procedure must be marked for replication so that the Replication Agent can identify and replicate invocations of that procedure in the primary database.

Replication Agents

A Replication Agent is the Sybase replication system component that captures the replicated transactions in a primary database and sends those transactions to a Replication Server for distribution to replicate databases.

Replication Agent reads a transaction log in the primary database and generates Log Transfer Language (LTL) output. LTL is the language that Replication Server uses to process and distribute replicated transactions throughout a replication system.

To provide more sophisticated replication features and generate more efficient LTL, you can configure Replication Agent to use information stored in the Replication Server System Database (RSSD) of the primary Replication Server.

Replication Agent retrieves the information it needs for transaction replication from the native transaction log maintained by the primary data server.

Replication Agent uses the log-based solution for primary databases in these primary database types:

Oracle
Microsoft SQL Server
IBM DB2 for Linux, UNIX, and Windows

Note: Procedure and DDL replication is not available for IBM DB2.

Replication Servers

The Replication Server that receives replicated transactions from a primary database (that is, directly from a Replication Agent) is called the primary Replication Server. The Replication Server that sends replicated transactions to a replicate database is called the replicate Replication Server.

Note: In a simple replication system, a single Replication Server can act as both the primary Replication Server and the replicate Replication Server.

After it receives LTL from a Replication Agent, the primary Replication Server sends the replicated transaction to a replicate database, either directly or through a replicate Replication Server. The replicate Replication Server converts the replicated transaction from the LTL it receives to the native language of the replicate database, and then it sends the replicated transaction to the replicate data server for processing. When the replicated transaction is processed successfully by the replicate database, the replicate database is synchronized with the primary database.

Each Replication Server holds transaction operations in a stable queue and delivers them as soon as possible to other Replication Servers or replicate databases. By doing this, Replication Server guarantees that every transaction successfully received from a Replication Agent is guaranteed to be delivered to appropriately subscribing replicate databases.

Each Replication Server uses a database called the Replication Server System Database (RSSD) to store replication system data and metadata. Replication Agent can use some of the information stored in the RSSD to provide advanced replication features.