RDF/IMP, IMPX, and ZLT System Management Manual

Online Database Synchronization
HP NonStop RDF/IMP, IMPX, and ZLT System Management Manual—524388-002
7-4
Considerations When Synchronizing Entire
Databases
Considerations When Synchronizing Entire Databases
The considerations for online synchronization fall into the following categories:
•
Duration of loads and getting the database prepared on the backup system
•
SYNCHDBTIME issues
•
CREATE/LOAD issues for NonStop SQL/MP tables and Enscribe files
•
Enscribe queue file issues
•
Different versions of NonStop SQL/MP on the primary and backup systems
•
Moving the duplicated tables and files to the backup system
Duration and Preparation Issues
As indicated in the steps described above, creating, loading, and placing the copy of
the database on the backup system can take quite a bit of time, and you cannot start
the updaters until the database is fully prepared on the backup system. This leads to
an issue that you must consider. While you are loading the data, and then getting the
database prepared on the backup system, you must run RDF with UPDATE OFF. This
means that audit will accumulate in the RDF image trails. When synchronizing
databases, you should configure image trail volumes that have a lot of free space for
image files.
The key problem you want to avoid is where your load and preparation steps take so
long that your image trails run out of space before you are able to start the updaters. If
the image trails fill, then this causes the extractors on the primary system to stop
sending audit data to the receivers because those receivers have no place to put the
audit data. Because the extractors pin audit trail files to avoid having TMF delete files
before the extractors have finished with them, this pinning, if it lasts long enough, could
lead in turn to the situation where no new transactions are allowed by the TMF product
on the primary system.
You can avoid the above situation by configuring enough image trails, and ensuring
that the image volumes have sufficient disk space. The more image trails you have,
the safer you are. Once the synchronization process has completed, you can always
reduce the number of image trails by stopping the RDF product and reconfiguring a
new RDF environment that has fewer image trails.
Alternatively, if your database is so big that it could take more time to load and prepare
than you have image space for, then you might want to synchronize one part of the
database at a time. When that operation has completed, you would then synchronize
the next portion. See below for the discussion on partial database synchronization and
the issues that pertain to it.