RDF System Management Manual

Managing RDF
HP NonStop RDF System Management Manual—524388-003
5-21
Takeover Operations
Takeover Operations
If the primary system fails and you want to switch application processing to the backup
system, you need to issue the TAKEOVER command from the backup system. The
TAKEOVER command causes RDF to shut down after bringing the backup database
to a consistent state.
The RDF Takeover Operation
When updating is enabled, updaters apply audit as soon as it is safe-stored in the
image trails on the backup system. In this respect, they apply audit without waiting to
determine if the associated transactions committed or aborted. At the moment when
you lose your primary system due to some unplanned outage, the updaters may have
applied audit for transactions whose outcomes were not resolved (committed or
aborted) on the primary system at the time the primary system failed. Alternatively, the
transactions may have been resolved on the primary system, but the extractor was
stopped before it could send the final outcomes to the backup system. The takeover
operation determines what audit needs to be backed out in order to bring the backup
database into a stable and consistent state. Audit is backed out of the backup
database during three possible undo passes, described below. For takeover
considerations in a ZLT environment, see Section 16, Zero Lost Transactions (ZLT).
Phase One Undo Pass
This is also known as Local Undo. Audit can be backed out of the backup database for
two possible reasons.
•
If an updater has applied audit for a transaction whose outcome is unknown, that
audit must be backed out.
•
If RDF is replicating audit from aux audit trails and if the final outcome is known,
but not all of the audit for the transaction from an aux trail reached the backup
system, that audit must be backed out.
Transactions that must be undone during this undo pass are stored in the ZTXUNDO
file in your Master Image Trail subvolume.
Phase Two Undo Pass
This is also known as File Undo. If one or more volumes failed on the primary system
and a transaction aborted, the TMF Backout process will backout the transaction on
the volumes that are still up, but it will be unable to backout the audit on the volumes
that are down. If the downed volumes come back online, the TMF Volume Recovery
process backs out the audit that the Backout process could not back out. If, however,
the primary system failed before Volume Recovery had enabled the downed volumes,
then, if you execute the RDF Takeover operation on the backup system, the updaters
execute an undo pass that will undo the audit the Volume Recovery would have
undone on the primary system if it had been able to.