RDF System Management Manual

Zero Lost Transactions (ZLT)
HP NonStop RDF System Management Manual—524388-003
16-9
ZLT Takeover Operations
ZLT Takeover Operations
If ZLT is configured and enabled when a TAKEOVER command is issued on the
backup system, the overall takeover operation executes in two phases.
Phase 1 (ZLT Processing)
RDFCOM stops all RDF processes on the backup system. If the standby and backup
systems are not the same system, RDFCOM copies the RDF configuration file on the
backup system to the standby system. RDFCOM then starts an RDF monitor process
on the backup system. That monitor then starts the extractor(s) on the standby system
and the receiver(s), purger, and updater(s) on the backup system.
Each extractor logs an event (901) reporting it is started for ZLT processing, starts a
special audit-fixup process to fix up the last file in the audit trail (see The Audit-Fixup
Process below), and sends all remaining audit records to its receiver. When an
extractor reaches the end of its audit trail, it sends a “ZLT finished” indication to its
receiver, and logs an event (900) reporting it has completed its ZLT task. When all
extractors are finished, they are terminated and deleted. Upon receiving the “ZLT
finished” indication, each receiver logs an event (903) reporting it has completed its
ZLT task, and tells its updater to commence normal takeover operations. When all
receivers have finished their ZLT processing, the overall takeover operation proceeds
to phase 2.
The Audit-Fixup Process
The audit-fixup process only ever runs on the remote standby system in an RDF/ZLT
environment and typically lasts only a few seconds. The audit-fixup process performs
file-fixup operations on audit-trail files on the remote mirror that have been left with the
CRASHOPEN flag set following a failure of the RDF primary node. The audit-fixup
process is started by an extractor whenever the extractor attempts to read an audit-trail
file that has the CRASHOPEN flag set. Unlike the other RDF processes, the audit-fixup
process does not persist for the duration of the RDF environment. The audit-fixup
process is started on demand by the extractor process, and terminates as soon as it
has performed the file-fixup processing on the audit-trail file.
This process does not run as process pair, but the extractor will start a new audit-fixup
process if the audit-fixup process is terminated due to a processor failure. No
configuration parameters are required for the audit-fixup process. The audit-fixup
process runs in the same CPU as the extractor primary process with a process priority
one less than the extractor priority.
Note. Before issuing the TAKEOVER command, you must have connected the remote mirrors
to the standby system. When the remote mirrors are connected to the standby system, the
audit records on the remote mirrors have no relationship to the audit trail on the standby
system. The remote mirrors are not part of the TMF configuration of the standby system.