Progress
Installation and Configuration Guide
Version 9
for UNIX


Shared-memory Configurations

Shared memory is an area in system memory that multiple users can access concurrently. Most UNIX systems use shared memory.

Shared memory systems run a version of Progress that uses the shared-memory architecture to provide superior performance and additional features.

On shared memory systems, more than one server can access a single database, service local or remote clients, and handle a variety of network protocols. Progress keeps resources shared by all database users in shared memory and lets multiple servers access those resources efficiently. Optionally, additional asynchronous I/O processes can offload I/O operations from each server, further improving resource utilization.

Progress uses semaphores and spin locks to synchronize the activities of server and self-service client processes that are connected to a database. Each process uses its semaphore or relies upon the spin lock when it must wait for a shared resource.

You can tune Progress performance by reconfiguring the size of the Database, Before-image (BI), and After-image (AI) buffers. See the "Shared Memory" section in "Memory and System Configuration," for more information about reconfiguring these buffers.

Local clients running multi-user Progress can access database resources directly, rather than through a database server. This eliminates client/server message exchange and task-switching overhead. Database requests do not have to be queued until a server can process them. Local direct-access clients are known as self-service clients.

To run shared-memory versions of Progress over a network, you need information regarding network-related system files, network configuration, and the startup parameters required to start remote clients. For more information about the network files and configuration, see the "Client/Server and Progress AppServer In the Network Environment" section and the "Preparing To Run Progress In a TCP/IP Network" section in this chapter. For information about starting remote clients, see Starting and Running Progress."

Figure 7–1 shows a sample shared-memory configuration.

Figure 7–1: Database Access On a Shared-memory System


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