Compaq Reliable Transaction Router - Manual (Page 22)

RTR Terminology
In this example, the frontend with the client and the router
reside on one node, and the server resides on the backend.
Frequently, routers are placed on backends rather than on
frontends. A further separation of workload onto three nodes is
shown in Figure 1–11.
Figure 1–11 RTR Deployed on Three Nodes
LKG-11209-98WI
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TR BE FE
DB
This three-node configuration separates transaction load onto
three nodes, but does not provide for continuing work if one
of the nodes fails or becomes disconnected from the others. In
many applications, there is a need to ensure that there is a
server always available to access the database.
In this case, a standby server will do the job. A standby
server (see Figure 1–12 is a process that can take over when
the primary server is not available. Both the primary and
the standby server access the same database, but the primary
processes all transactions unless it is unavailable. The standby
processes transactions only when the primary is unavailable. At
other times, the standby can do other work. The standby server
is often placed on a node other than the node where the primary
server runs.
1–12 Introduction