Tuning Tips for Applications That Use SAS/SHARE Software

Concurrent Access: Update versus Read-only

Many applications use several SAS files. It is to your advantage if, while designing your application, you identify and divide the following:

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 might 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 environments 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 dividing files into read only and concurrently updated libraries:

A SAS file that is accessed through a server usually 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 might be a subset instead of 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 cannot be updated while a user executes the part of the application that uses that file.

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