RDF/IMP, IMPX, and ZLT System Management Manual

Online Database Synchronization
HP NonStop RDF/IMP, IMPX, and ZLT System Management Manual—524388-002
7-5
Considerations When Synchronizing Entire
Databases
SYNCHDBTIME Issues
With the SYNCHDBTIME option in the INITIALIZE RDF command, there are three
special cases you might need to consider:
•
Enscribe create operations
•
NonStop SQL/MP Shared Access DDL operations
•
TMF shutdown operations
Enscribe Create Records
If you created the same Enscribe file on the primary and backup systems prior to
execution of the INITIALIZE RDF command, and if the extractor’s restart position is
located before the audit record for the create operation on the primary system, you
must remember to purge that file on the backup system. Otherwise, when the updater
tries to replicate the create operation, it will report a File System error 10 (File Already
Exists) and restart. It continues to restart and attempt to create the file until you purge
the existing file on the backup system.
Stop-RDF-Updater Records
Stop-RDF-Updater records in the MAT are associated with committed NonStop
SQL/MP DDL operations performed on the primary system with the WITH SHARED
ACCESS option. Although such operations can be performed on the primary system
without stopping your applications, they must be performed manually on the backup
system after all updaters have shut down in response to the same Stop-RDF-Updater
record.
As a general rule, you should not initialize the RDF subsystem to a synchdbtime if you
recently performed a NonStop SQL/MP operation with SHARED ACCESS on the
primary system. For example, suppose you have a NonStop SQL/MP table (tableA)
that contains the range of keys A through Z and you just moved its partition boundary
such that tableA now contains only the keys A through M and a new table (tableB)
contains the keys N through Z. Suppose also that you performed this operation
manually on the backup system.
If you then initialize the RDF subsystem to a point in the MAT prior to the Stop-RDF-
Updater record associated with the partition boundary change and an updater
encounters audit information associated a key N through Z, the updater will report an
error because it will try to apply the audit information to tableA (which used to contain
it, but now does not), and the audit information will not be applied to the backup
database. In this particular case the database is not corrupted, but data corruption
could occur for other NonStop SQL/MP DDL SHARED ACCESS operations.
If you did recently perform a NonStop SQL/MP operation with SHARED ACCESS on
the primary system and you want to initialize the RDF subsystem to a synchdbtime,
you must specify a synchdbtime such that the starting position in the MAT is after the
Stop-RDF-Updater record.