Compaq Reliable Transaction Router Getting Started page 16

RTR Terminology
Figure 1–3 Roles Symbols
The mapping between nodes and roles is done using a facility.
Facility
An RTR facility is the user-defined name for a particular
configuration whose definition provides the role-to-node map for
a given application. Nodes can share several facilities. The role
of a node is defined within the scope of a particular facility. The
router is the only role that knows about all three roles. A router
can run on the same physical node as the frontend or backend,
if that is required by configuration constraints, but such a setup
would not take full advantage of failover characteristics.
Figure 1–4 Facility Symbol
A facility name is mapped to specific physical nodes and their
roles using the CREATE FACILITY command.
Figure 1–5 shows the logical relationship between client
application, server application, frontends (FEs), routers (TRs),
and backends (BEs) in the RTR environment. The database is
represented by the cylinder. Two facilities are shown (indicated
by the large double-headed arrows), the user accounts facility
and the general ledger facility. The user accounts facility uses
three nodes, FE, TR, and BE, while the general ledger facility
uses only two, TR and BE.
Clients send messages to servers to ask that a piece of work be
done. Such requests may be bundled together into transactions.
An RTR transaction consists of one or more messages that have
been grouped together by a client application, so that the work
done as a result of each message can be undone completely, if
some part of that work cannot be done. If the system fails or is
1–6 Introduction
FE
BE
TR