RDF System Management Manual for J-series and H-series RVUs (RDF Update 13)

15 Process-Lockstep Operation
The RDF/IMPX products include the process-lockstep operation, which is process-based. That is,
when a process invokes the lockstep operation for a business transaction, the process must wait
until all audit records associated with that business transaction are safely stored in image trails on
the backup system before continuing.
Process-lockstep is not needed with RDF/ZLT because ZLT functionality provides means whereby
no committed data is ever lost during an unplanned outage. Hence, ZLT functionality is a more
efficient means of achieving the same result as process-lockstep. Process-lockstep can be used with
RDF/ZLT, but does not add anything that ZLT functionality does not already provide.
A lockstep operation consists of these steps.
1. A process starts a business transaction and does database updates.
2. The process calls endtransaction to commit the work.
3. The process issues a DoLockstep procedure call.
4. The DoLockstep procedure communicates with an RDF gateway process.
5. The gateway starts a lockstep transaction against an RDF lockstep file.
6. The gateway communicates with the RDF subsystem regarding the lockstep transaction.
7. The RDF subsystem tells the gateway when lockstep audit has been safely stored on the backup
system.
8. The gateway returns status to the DoLockstep procedure.
9. DoLockstep returns status to the process.
Figure 13 RDF Lockstep Operation
Primary System Backup System
Purger
Master Receiver
Database
$D1 - $D10
Database
$D11 - $D15
Updaters
$UP11 - $UP15
Master
Image
Trail
Auxiliary
Receiver
Secondary
Image
Trail
Secondary
Image
Trail
RDFCOM
User App
$ZLGSW
Master
Audit
Trail
Monitor
Database
$D1 - $D10
Database
$D11 - $D15
Master Extractor
Auxiliary
Extractor
Auxiliary
Audit
Trail
Updaters
$UP1 - $UP10
Thus, although the business transaction is actually committed on the primary system (and the file
locks or table locks are released), the process cannot continue processing until all of the audit data
associated with that transaction is safely stored in the image trails on the backup system).
299