Compaq Reliable Transaction Router manual Shadow Servers

RTR Server Types

Figure 1–16 shows a simple shadow configuration. The main (BE) Server at Site 1 and the shadow server (Shadow) at Site

2 both receive every transaction for the data partition they are servicing. Should Site 1 fail, Site 2 continues to operate without interruption. Sites can be geographically remote, for example, available at separate locations in a wide area network (WAN).

Figure 1–16 Shadow Servers

Terminals	Frontends (FE)
	FE

Client

FE

Client

FE

Client

Routers (TR)

TR

Backends (BE)	Database (DB)
BE - SITE 1
Server	DB
BE - SITE 2
Shadow	DB

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Concurrent server

Note that each shadow server can also have standby servers.

The concurrent server is an additional instance of a server application running on the same node. RTR delivers transactions to a free server from the pool of concurrent servers. If one server fails, the transaction in process is replayed to another server in the concurrent pool. Concurrent servers are designed primarily to increase throughput and can exploit Symmetric Multiprocessing (SMP) systems. Figure 1–17, Concurrent Servers, illustrates the use of concurrent servers sending transactions to the same partition on a backend, the partition A-N.

Concurrent servers allow transactions to be processed in parallel to increase throughput. Concurrent servers deal with the same database partition, and may be implemented as multiple

1–18Introduction