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

HP NonStop RDF/IMP and IMPX System Management Manual—524388-001
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Online Database Synchronization
With RDF/IMPX you can synchronize entire databases or selected volumes, files,
tables or even partitions while your applications continue to run.
Overview
The RDF online database synchronization protocol consists of the following general
steps (the details of which are discussed later in this section):
•
initialize the RDF configuration with the SYNCHDBTIME option.
•
issue a START RDF, UPDATE OFF command.
•
create an empty copy of the database
•
load the data from the actual database into the copy with shared access. Because
the load operation with shared access reads through transaction locks held by
applications, the resulting file is inconsistent with respect to transactions, but it is
consistent with respect to its physical state.
•
When the loads have completed and the copy of the database is on the backup
system, issue a START UPDATE command. As the updaters start applying audit,
they put the backup database to a consistent state with regard to transactions.
The RDF online database synchronization protocol can be used to synchronize entire
databases or selected parts of databases. The operations can be complex, depending
upon the database system being used (NonStop SQL or Enscribe), the file types being
used (key-sequenced and relative), and whether you need to synchronize an entire
database or just selected portions. If you need to synchronize entire databases, you
should carefully read the sections “Synchronizing Entire Databases Online” and
“Considerations When Synchronizing Entire Databases” first.
Because you must run RDF with UPDATE OFF while you load the empty copy of the
database, audit data will collect in the RDF image trails before you can eventually start
the updaters. Therefore, if your database is very large, you might want to consider
synchronizing several volumes at a time.
Note. Entry-sequenced files and tables, unstructured files, and SQL tables that have
SYSKEYs or clustering keys cannot be synchronized with the methods described
below. For those types of files, you must synchronize them offline.
Note.
RDF does not replicate SQL catalogs. Therefore, if you are synchronizing SQL
tables, you may need to create SQL catalogs manually on the backup system.