Many applications use several SAS files. It is to your advantage if,
while designing your application, you identify and segregate:
- the set of files which must be updatable by more
than one user at a time
- the files that will be updated by only one user,
but while other users are reading the files
- the files that will be updated so infrequently
that access to those files by all users is practically read-only
The files in the first group are excellent candidates
for access through a server. The files in the second group are often good
candidates for access through a server, but for some applications the performance
improvement from not accessing the files through a server may make it worthwhile
to use a more complicated procedure to update those files while the users
are not around. The files in the third group are almost always poor candidates
for access through a server because all of the operating systems that SAS
runs under provide shared read-only access to files, and that direct access
is almost always faster than access through a server.
Here is a summary of the advantages and disadvantages
of segregating files into read only and concurrently updated libraries:
- A SAS file that is accessed through a server generally
costs more, in terms of computing resources, for users of the application
to use than a SAS file that is stored in a library that is accessed directly
by the users.
- Reduced traffic through a server optimizes response
time for the users of the concurrently updated files.
- Simpler, more direct access to read-only copies
of files reduces the cost of an application's query and reporting functions.
Note that such a copy may be a subset rather than the entire file.
- A SAS file that is accessed through a server can
be updated while it is being queried or reported on.
- Copies of files require disk space.
- A file in a SAS library that
is accessed directly
by users can not be updated while a user executes the part of the application
that uses that file.
Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
