RDF System Management Manual

Introducing RDF
HP NonStop RDF System Management Manual—524388-003
1-26
Reciprocal and Chain Replication
Although all the updater restart locations are in AA000015, none of the image files from
AA000002 through AA000014 can be purged while T1000 is active or aborting
because they will be required if T1000 needs to be backed out during an RDF takeover
or stop-update-to-timestamp operation. Note that this is true for both trails, even
though none of the updaters on one trail have ever been involved with T1000. If an
UNDO pass becomes necessary, all updaters must perform that pass in search of any
audit records associated with T1000 (they must go back in each image trail to the point
where T1000 began: AA000002 in this example).
The purger process exists to avoid having the receiver keep track of all this
information, which could impact extractor-receiver throughput significantly. The purger
process interacts with the updaters to determine when image files can be purged.
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.
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.