RDF/IMP and IMPX System Management Manual (RDF 1.4+)

Introducing RDF

HP NonStop RDF/IMP and IMPX System Management Manual—524388-001

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Reciprocal and Chain Replication

Figure 1-7. Reciprocal Replication

System \A System \B

RDF Subsystem 1

Primary DB 1 ----------------------------------> Backup DB 1

RDF Subsystem 2

Backup DB 2 <---------------------------------- Primary DB 2

Thus, you have a primary database for RDF subsystem 1 on

system \A (primary DB 1) and a primary database for RDF

subsystem 2 on system \B (primary DB 2).

Figure 1-8. Chain Replication

System \A System \B System \C

RDF Subsystem 1

Primary DB 1 ---------> Backup DB 1

Primary DB 2 ----------> Backup DB 2

RDF Subsystem 2

Thus, system \B is both the backup system in RDF subsystem 1

and the primary system in RDF subsystem 2.

With the NonStop RDF/IMP(X) product, the updaters generate audit records as they

replicate data to the target files and target tables, and these audit records are internally

marked as updater-generated audit records. The extractors filter out all updater-

generated audit. Thus, under normal circumstances, the extractors do not send

updater-generated audit to their backup systems for replication.

Consider the following example. Assume that Primary DB 1 and Backup DB 2 are both

located on $DATA on \A, and assume that Primary DB 2 and Backup DB 1 are also

located on $DATA on \B. Using the reciprocal example, suppose your application does

an update on \A to Primary DB 1. The extractor of RDF Subsystem 1 sees that the

update was for $DATA and sends that update to \B where the updater applies that

update to Backup DB 1. This update generates an audit record that goes into the audit

trail on \B and is marked as updater-generated. The extractor for RDF Subsystem 2

reads the audit trail looking for audit associated with $DATA. When it reads the record

generated by the udpater, it sees the update was associated with $DATA, but it also

sees that the record was updater-generated, which causes the extractor to filter that

record out and not send it to \A. This is correct and desired behavior.