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Starting and Setting Up RTR
2.12 How RTR Selects Processing-states (Roles) for Nodes
2.12 How RTR Selects Processing-states (Roles) for Nodes
This section discusses how RTR assigns roles to backend node partitions, and
how routers are selected.
2.12.1 Role Assignment for Backend Node Partitions
RTR assigns a primary or secondary processing state to a partition (or a key-
range definition), consisting of one or more server application channels, which
may or may not share a common process. All such server channels belonging to
a given partition will have the same processing state on a given node. However,
the processing state for the same partition will normally be different on different
nodes. The exception is the case of the standby processing state. Because a given
partition can have multiple standby nodes, several of these nodes may be in this
state.
RTR determines the processing state of a given partition through the use of
a globally managed sequence number for that partition. By default, the RTR
master router will automatically assign sequence numbers to partitions during
startup. When a server is started up on a backend node and declares a new
partition for that node, the partition initially has a sequence number of zero.
When the partition on that backend makes an initial connection to the master
router, the router increases its sequence number count for that partition by
one and assigns the new sequence number to the new backend partition. The
active node with the lowest backend partition sequence number gets the primary
processing state in both shadow and standby configurations. That node is also
referred to as the primary node, though the same node could have a standby
processing state for a different partition.
Under certain failover conditions, backend partitions may either retain their
original sequence number or be assigned a new sequence number by the router.
If a failure is caused by a network disruption, for example, a backend partition
will retain its sequence number when it reconnects with the router. However, if
the backend node is rebooted or RTR is restarted on the backend node, a new
sequence number will be assigned by the router to any partitions that start up on
that node. Routers will only assign new sequence numbers to backend partitions
that have a current sequence number of zero, or if the backend partition is
joining an existing facility and has a sequence number that conflicts with another
backend partition on another node.
Sequence number information can be obtained from the SHOW PARTITION
command. In the output of this command the sequence number is indicated
by the relative priority. The following example shows a sample of the SHOW
PARTITION command from a router partition. This example shows that the
backend partition called Bronze has a sequence number of 1, and backend
partition called Gold has a sequence number of 2.
Router partitions on node SILVER in group test at Mon Mar 22 14:51:16 1999
State: ACTIVE
Low bound: 0 High bound: 4294967295
Failover policy: fail_to_standby
Backends: bronze,gold
States: pri_act,sec_act
Relative priorities: 1,2
Primary main: bronze Shadow main: gold
2–18 Starting and Setting Up RTR