Replicator Components
This section provides an overview of how Ingres Replicator components work together to process a replication from one database to another. This description is intended to provide the background necessary to maintain and troubleshoot Ingres Replicator. It discusses full peer to full peer or full peer to protected read-only configurations, and assumes that there are no collisions.
Ingres Replicator consists of three distinct components that participate in the actual replication of data:
• Change Recorder
The Change Recorder is a DBMS Server component that captures information about each update to a replicated table as part of the user transaction. The Change Recorder inserts a row in the shadow table and, if necessary, in the archive table, for each base table row manipulated by the user. It also adds an entry to the input queue for each such row.
• Distribution threads
When the user commits the transaction, a distribution thread in the DBMS Server reads the input queue and for each input row and destination, it inserts an entry into the distribution queue. The input rows are deleted and the Replicator Server is alerted.
• Replicator Server
The Replicator Server is a separate process that reads the distribution queue and propagates each distribution queue row to the corresponding target. At the end of each set of rows comprising a user transaction, the distribution rows are deleted and two phase commit is used to secure the transmitted transaction.
In addition, Ingres Replicator includes a management component—either Visual DBA or the Replicator Manager, plus additional utilities that provide operational support.