Q Replication and Event Publishing

Q subscriptions

You create objects called Q subscriptions to define how data from a single source table is replicated to a single target table or is passed to parameters in a stored procedure for data manipulation.

The Q subscription tells the replication programs which changes to capture from the source table, what queues to use for sending and receiving change messages, and how to process the messages. Figure 1 shows how a Q subscription connects a source table to a target table. Q subscriptions can also map DB2® sources to DB2 targets and DB2 sources to some non-DB2 targets. Figure 2 shows how a Q subscription connects a source table to a target table for non-DB2 targets.

Figure 1. Q subscription. Changes from a source table are replicated over WebSphere MQ queues to a target table.

Figure 2. Q subscription for non-DB2 targets. Changes from a source table are replicated over WebSphere MQ queues to a nickname that is mapped to a table in the non-DB2 target.

The graphic shows a Q subscription for non-DB2 targets.

You must create a Q subscription for each source-to-target pair. Each Q subscription is a single object that identifies the following information:

The source table that you want to replicate changes from.
The target table or stored procedure that you want to replicate changes to.
The columns and rows from the source table that you want to be replicated.
The replication queue map, which names the WebSphere MQ queues that transport information between the source server and target server.

For Q subscriptions, you can specify the following options:

Which columns to replicate and how they map to columns at the target table (or to parameters in a stored procedure).
A search condition to determine which rows from the source table are replicated.
How the Q Apply program detects and responds to conflicts between rows at the source and target database.
How the target table will be loaded with data from the source table.

Q subscriptions for either bidirectional or peer-to-peer replication must replicate all columns in the source table. These types of replication also require specific types of conflict detection and conflict handling.

If you make changes to a Q subscription after you create it, you need to reinitialize it so that the Q Capture program reads the changes.

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Last updated: 2013-10-25