HP NonStop G-Series - Manual (Page 51)

SDR Operations
HP NonStop SQL DDL Replicator User’s Guide —545799-005
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Distributed Table Replication
An RDF takeover can occur only if the primary system has failed (or is unavailable on
the Expand network) or if RDF has been stopped on the primary system. Either of
these events will cause the SDR updaters started from the primary system to shut
down.
When you issue the RDF TAKEOVER command, the SDR monitor on the backup
system immediately starts an SDR updater for that RDF configuration. If there are any
SDR-captured DDL operations in the remaining RDF image trail, RDF will shut down
on each SRU audit record, SDR will execute the DDL operation and then restart the
RDF takeover. Eventually, RDF will enter the “Takeover Complete” state and both RDF
and SDR will shut down.
Note that, for complex RDF topologies, the SDR monitor can start SDR updaters for
both primary and takeover RDF configurations on the same system.
Distributed Table Replication
If a table or index has partitions and indexes on remote systems, the DDL capture
process has written a SRU audit record to the audit trail of each system that has a
partition or an index of the table. On each one of those systems, RDF is expected to
enter the “Update NSA Stopped” state for the same file name. (Actually, each SRU file
name contains a primary volume on the remote system, but the
ZASDRnnn.AAmmmmmm part of the file name will be the same.)
The SDR depot record contains a list of all systems that received an SRU audit record,
including the volume name used in each remote SRU audit record. SDR must wait until
all such systems have entered that state for the correct file name.
In order to translate distributed table DDL operations, SDR needs an accurate
description of the RDF network, which is a list of RDF control subvolumes and their
primary and backup systems. This must be specified in either the SDR configuration, in
networks where RDF IMP is running, or in the RDF configuration, where RDF IMP/X is
running.
SDR accesses the RDF configurations for each of the systems that are referenced in
the DDL operation, and uses that information to translate the DDL to reference the
appropriate backup systems and volumes.
Then, SDR is ready to execute the DDL operation and restart RDF updating on all of
the listed systems.