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This chapter gives a brief overview of the facilities provided by
Fileshare and also describes how Fileshare works.
Fileshare is best suited to applications that share data files,
concurrently, between many users, across a network. It supports all of the
functionality provided by the base COBOL file handling system and provides
several additional features:
- Reduced network traffic
- Transaction processing
- Rollforward recovery logging
- Logon and file open security checks
The ability of any one application to take advantage of these features
depends on:
- The way the application processes the shared data files
- The type of data files the application shares
- The operating system on which the Fileshare Server is running
- The communications protocol being used between the Fileshare Client and
the Fileshare Server
You do not need to make any program source code changes to use the basic
Fileshare system. Source code changes are only needed to take advantage of
some of the advanced features provided by Fileshare.
Using the base COBOL file handling system, a typical COBOL I/O request to
a shared data file causes the file handler to make several accesses to that
data file across the network. See Figure 1-1.
Figure 1-1: Conventional network
With Fileshare, a program that needs to access a data file has its request
processed by the File Handling Redirector (FHRedir) module. The FHRedir
module sends the request over the network to a Fileshare Server that performs
the low-level I/O operations and then passes the result of the I/O operation,
including the file status, back to FHRedir. FHRedir returns the result to the
program. See Figure 1-2.
Figure 1-2: Fileshare network
A Fileshare System is made up of:
Fileshare Clients
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A Fileshare Client comprises a user program, making data file I/O
requests, via the FHRedir module. FHRedir redirects the I/O requests to a
Fileshare Server.
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Fileshare Servers
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A Fileshare Server runs on the same machine as the data files that you
want to access. The Fileshare Server accepts requests across the network
from the Fileshare Client, processes them by calling a local copy of the
Micro Focus File Handler and then returns the result to the Fileshare
Client. |
Notes:
- The Fileshare Server and the Fileshare Client can be running on the same
physical machine. For example, with a multi-tasking operating system such as
Windows, the Fileshare Client can run in one session and the Fileshare
Server can run in another session. Using this method, you can develop
Fileshare applications on a single PC without actually sending data across a
network. You should be aware, however, that performance improvements will
not be observed, as no network is being used.
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You can also run the Fileshare Server in the same session as the
Fileshare Client using the single user mode of operation. This enables you
to take advantage of advanced Fileshare features such as transaction
processing without the need for a network or multiple sessions. For more
information on the single user mode of operation, see Single User Mode.
Since a single Fileshare Server processes all the requests from several
Fileshare Clients, it can use a single copy of the Micro Focus File Handler,
regardless of how many users are accessing the Fileshare Server. This has
several advantages:
- The Fileshare Server can open the data files exclusively making full use
of both its own cache and the operating system's cache.
- The Fileshare Server does not need to obtain semaphores on the data
file. Normally semaphores are needed to control concurrent access to shared
data files.
- The Fileshare Server can process record locks internally without the
need to make calls to the operating system.
Copyright © 1998 Micro Focus Limited. All rights reserved.
This document and the proprietary marks and names
used herein are protected by international law.
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