Replicator Concepts
To create a successful replication scheme, it is important to understand concepts and terms used in Replicator.
Key Ingres Replicator concepts are as follows:
Collision
A collision is an event that occurs when more than one user updates the same replicated row in different databases. Ingres Replicator can preserve the history of changes made to each replicated row. If the same rows in two databases do not match in the last transaction, Ingres Replicator detects a collision.
Consistent Distributed Data Set (CDDS)
A CDDS defines what data is replicated and where it resides.
The CDDS is the unit of organization in Ingres Replicator. Various processes, such as collision and error handling, are specified at the CDDS level.
CDDS Target Type
A target type defines which database within a CDDS is allowed to alter the data and how Ingres Replicator acts on each database within the CDDS.
The target types are:
• Full peer--generates changes to be replicated, accepts replicated changes and can detect collisions
• Protected read-only--accepts replicated changes and can detect collisions
• Unprotected read-only--accepts replicated changes but cannot detect collisions
A CDDS has a target type defined in every database that is contained in the CDDS. You must define target types for each CDDS. For more information, see
CDDS Target Types.
Data Propagation Path
A data propagation path defines what route the data takes to reach target databases within a CDDS.
Replicated transaction key (replication key)
To identify information specific to Ingres Replicator during processing of a replicated row, the system generates a key for each such row.
The key consists of:
• A database number that identifies the replicated database that manipulated the row
• The ID of the DBMS Server transaction that manipulated the row
• The sequence number within the transaction
Other concepts...
• Change Recorder
• distribution threads
• Replicator Server
• base table
• shadow table
• archive table
• input queue
• distribution queue