HP Reliable Transaction Router - Manual (Page 30)

RTR Server Types
Standby server
The standby server remains idle while the RTR primary
backend server performs its work, accepting transactions and
updating the database. When the primary server fails, the
standby server takes over, recovers any in-progress transactions,
updates the database, and communicates with clients until
the primary server returns. There can be many instances of a
standby server. Activation of the standby server is transparent
to the user.
A typical standby configuration is shown in Figure 1–12,
Standby Server Configuration. Both physical servers running
the RTR backend software are assumed by RTR to connect
to the same database. The primary server is typically in use,
and the standby server can be either idle or used for other
applications, or data partitions, or facilities. When the primary
server becomes unavailable, the standby server takes over and
completes transactions as shown by the dashed line. Primary
server failure could be caused by server process failure or
backend (node) failure.
Standby in a
cluster
The intended and most common use of a standby server
is in a recognized cluster environment. In a noncluster or
unrecognized cluster environment, seamless failover of standbys
is not guaranteed. For RTR, clusters supported by OpenVMS
and Tru64 UNIX are recognized clusters, whose processing is
controlled by a lock manager. Windows and Sun clusters can use
disk-sharing, unrecognized cluster technology.
Standby servers are ‘‘spare’’ servers that automatically take over
from the main backend if it fails. This takeover is transparent to
the application.
Figure 1–14 shows a simple standby configuration. The two
backend nodes are members of a cluster environment, and are
both able to access the database.
For any one key range, the main or primary server (Server
application) runs on one node while the standby server (Standby
application) runs on the other node. The standby server process
is running, but RTR does not pass any transactions to it. Should
the primary node fail, RTR starts passing transactions to the
Standby application.
1–18 Introduction