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Starting and Setting Up RTR
2.12 How RTR Selects Processing-states (Roles) for Nodes
8. The network connection to node Gold is reestablished. The partition on Gold
retained its original sequence number of 2 and retains the primary role while
the partition on Bronze reassumes the secondary role.
Alternately, the roles of backend nodes can be specifically assigned with the
/PRIORITY_LIST qualifier to the SET PARTITION command. In the previous
example the /PRIORITY_LIST qualifier can be used to insure that when Bronze
fails and then returns to participate in the facility it then becomes the active
primary member. To insure this, the following command would be issued on both
backend systems immediately after the creation of the partition:
SET PARTITION test/PRIORITY_LIST=(bronze,gold)
It is recommended that the same priority list order be used on all partition
members. If a different list is used then the router will determine the sequence
number for conflicting members through the order in which those members joined
the facility. For example, if the above command were issued only on Bronze
and Gold had the opposite priority list, then the router would assign the lower
sequence number to the backend that joined the facility first.
The /PRIORITY_LIST feature is very useful in cluster configurations. For
example, Site A and Site B each contain 2-node clusters. The facility is configured
such that at Site A, Node-A1 has the primary active partition and Node-A2 has
the standby partition. At Site B, Node-B1 is the secondary active partition and
Node-B2 has the standby of the secondary. The partition could be defined such
that the standby node, Node-A2, would become active if the primary node were
to fail. For example, issuing the following command on all four nodes for this
partition guarantees that the specified list is followed when there is a failure.
SET PARTITION test/PRIORITY_LIST=(Node-A1,Node-A2,Node-B1,Node-B2)
Using the SHOW PARTITION command from the router, this partition would be
as follows:
Router partitions on node SILVER in group "test" at Mon Mar 22 17:22:06 1999
State: ACTIVE
Low bound: 0 High bound: 4294967295
Failover policy: fail_to_standby
Backends: node-a1,node-a2,node-b1,node-b2
States: pri_act,standby,sec_act,standby
Relative priorities: 1,2,3,4
Primary main: node-a1 Shadow main: node-b1
However, the partition could also be configured so that the secondary active node,
Node-B1, would become the primary node if the original primary system were
to fail. This is controlled with the /FAILOVER_POLICY qualifier to the SET
PARTITION command. The default is /FAILOVER_POLICY=STAND_BY.
2–20 Starting and Setting Up RTR