RDF/IMP and IMPX System Management Manual (RDF 1.3+)

Lockstep Operation

Compaq NonStop™ RDF/IMP and IMPX System Management Manual—522204-001

14-7

Reenabling Lockstep

To reenable lockstep processing:

1. Change DISABLE to ENABLE in the STARTUPMSG attribute script.

2. Manually delete the RDF lockstep gateway process from SCF.

3. Run the changed SCF script.

When SCF restarts the gateway, lockstep processing is enabled.

Lockstep Performance Ramifications

By definition, a lockstep operation will increase the reponse time of your application

because, after having invoked DoLockstep, the application must wait for the data to

become safely stored in the backup system’s image trail. The extractor and receiver

processes have been streamlined to facilitate lockstep processing, but a short delay is

unavoidable.

Expand problems or CPU failures that trigger extractor and receiver restart operations

could also increase response times.

As described under Multiple Concurrent Lockstep Operations

, the RDF gateway only

ever has a single lockstep transaction in progress at any one time. If called while a

lockstep transaction is in progress, the RDF gateway merely queues the request.

Consequently, if an application process issues a DoLockstep request immediately after

the gateway has started a lockstep transaction, that request must wait to be performed

until the current lockstep transaction is commited on the backup system. That could also

increase response times.

Lockstep and Auxiliary Audit Trails

You cannot use lockstep processing in an RDF subsystem that is protecting auxiliary

audit trails.

Lockstep and Network Transactions

You cannot use lockstep to protect data associated with network transactions because the

lockstep protocol only pertains to operations on a single system. If lockstep is used with

network transactions, consistency between lockstep operations and the distributed

application database files cannot be guaranteed after an RDF takeover.