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

Online Database Synchronization
Compaq NonStop™ RDF/IMP and IMPX System Management Manual—522204-001
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Updater Phases
Updater Phases
You cannot start the updaters until the extractor has completed phase 2.
Prior to phase 1, an updater applies all audit information to the backup database
regardless of the commit/abort status of the associated transactions. Thus, it might apply
audit information generated by the backout process, thereby performing undo
operations.
The updater phases of online database synchronization are as follows:
Phase 1
When an updater encounters the extractor’s synch-phase-1-complete record, this means
that the updater is processing audit records that were generated after the load or backup
operation completed on the primary system. Synchronization of the databases is still not
complete, however, because the updater must still process audit records for transactions
that were active during the load or backup operation.
Upon completion of phase 1, the updater logs message 844.
Phase 2
Phase 2 completes when the updater encounters the synch-complete image record in the
image trail. At that time the updater has processed all audit information that might have
been generated during the load or backup operation, and synchronization is complete for
the associated database volume.
Upon completion of phase 2, the updater logs message 782.
Restart Considerations During Online Database
Synchronization
A number of circumstances can cause the extractor to restart during online database
synchronization, such as a primary CPU failure affecting either the extractor or receiver
process. Whenever the extractor encounters a restart condition it automatically recovers
and resumes its synchronization functions. Where it resumes, however, depends upon
where it was when the restart condition occurred.
•
If the restart condition occurs prior to the start of phase 1, the extractor resumes
wherever the receiver tells it to.
•
If the restart condition occurs after phase 1 has begun, the extractor may choose to
resume at an earlier position than the receiver tells it to. It does this to ensure that it
has handled all committed and aborted transactions correctly. If the extractor does
resume at an earlier position, it logs message 775. Additionally, regardless of
Note. If you are replicating only the master audit trail (MAT), you may start the updaters as
soon as the extractor issues its 782 event message. If you are also replicating one or more
auxiliary audit trails, however, you must also wait for all of the auxiliary extractors to report 0:00
RTD times before starting the updaters.