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

Network Transactions
HP NonStop RDF/IMP and IMPX System Management Manual—524388-001
13-12
Takeover and the RETAINCOUNT Value
Takeover and the RETAINCOUNT Value
In order for all systems in an RDF network to execute phase 3 takeover processing
correctly, you must ensure that all image data potentially needed for undo is available
on each system. The way to achieve that is to set the purger’s RETAINCOUNT to an
acceptable value on each system. For a complete discussion about this attribute and
how it works, refer to Section 10, Triple Contingency. (The same RETAINCOUNT
guidelines that apply to a triple contingency environment also apply to an RDF network
environment.)
Note that if you have not set the RETAINCOUNT properly and image files have been
purged that are subsequently needed for phase 3 takeover processing, the takeover
operations on the systems where the image data is missing might fail. In such a case,
your entire distributed database across all RDF backup systems could be
compromised with inconsistent data.
Network Configurations and Shared Access
SQL DDL Operations
Under certain circumstances after a shared access SQL DDL operation, takeover
network undo processing leads to an abort with database corruption.
To avoid this problem, use the following protocol when performing shared access SQL
DDL operations in a network environment:
1. Issue the RDFCOM STOP RDF command on the primary system where you plan
to perform the shared access SQL DDL operation.
2. From TMFCOM STATUS TRANSACTIONS, collect all the network transactions
that are currently in progress.
3. Wait until all transactions observed in step 2 have completed and are no longer
listed.
4. For all other primary nodes in your RDF network, run RDFCOM STATUS RDF
commands.
5. When all other RDF subsystems in the RDF network list 0:00 extractor RTD times,
issue the RDFCOM START RDF command on the system where you had stopped
RDF.
6. Perform your shared access SQL DDL operation on your primary system.
7. Follow the normal method for replicating shared access SQL DDL operations on
your backup system.
Network Validation and Considerations
A set of rules has been devised to ensure that all RDF subsystems in your configured
RDF network are consistent with each other.