IBM Licensed Programs: Database Products 535
IBM Licensed Programs: Database Products
source tables, for example, for a full refresh. Supporting update and refresh copying provides
greater flexibility and automation in a replication environment.
The Apply component also enhances the data to your specifications as it copies data to the
targets. The full power of SQL can be exploited to:
• Create new columns
• Summarize data
• Translate data
• Join data
Run-time processing statements can be defined using SQL statements and stored
procedures before and after the Apply program processes the replication subscription. The
run-time processing statements can be run at the source server before the answer set is
retrieved and at the target server before and after the answer set is applied. The stored
procedures use the SQL CALL statement, newly supported by IBM Replication, without
parameters. The run-time procedures are executed together in a single unit-of-work.
Acceptable SQLSTATEs can be defined for each processing statement as well.
The Apply component allows the creation of:
• Read-only copies
– User copy tables, which represent source data at a particular point in time
– Point-in-time tables, which represent source data at a particular point in time plus
some overhead columns
– History tables
– Staging tables, which can be used as a source for further copies without recapturing
changes, supporting a consistent data environment, and providing flexibility in data
distribution across the network
• Updatable copies
– Replica tables: Updates to a Replica table are automatically applied to the original
source table of the Replica, provided no conflicts are detected.
The Apply component running at the replica site, detects update conflicts after they
occur during the subscription cycle. When transactions are rejected, the Apply
compensates the transactions at the replica site. During this process, the Apply
inserts rejection codes for every rejected transaction in the control table. Conflict
detection is provided at three levels: no detection, standard detection, and enhanced
detection, specified while defining the replication source. When a conflict is detected
and compensated, the replication subscription is considered failed. All related
transactions are checked for conflicts and are also rejected.
After the Apply completes the subscription cycle, the ASNDONE exit indicates that the
cycle is complete and whether there were conflicts. An ASNDONE user exit can be
used to manage recovery from conflicts.
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