Optimizing System Performance

Collecting and Interpreting Performance Statistics

Using the FULLSTIMER and STIMER System Options

The FULLSTIMER and STIMER system options control the printing of performance statistics in the SAS log. These options produce different results, depending on your operating environment. See the SAS documentation for your operating environment for details about the output that SAS generates for these options.

The following output shows an example of the FULLSTIMER output in the SAS log, as produced in a UNIX operating environment.

Sample Results of Using the FULLSTIMER Option in a UNIX Operating Environment

   NOTE: DATA statement used:
         real time           0.19 seconds
         user cpu time       0.06 seconds
         system cpu time     0.01 seconds
         Memory                            460k
         Semaphores    exclusive 194 shared 9 contended 0
         SAS Task context switches         1   splits 0

The STIMER option reports a subset of the FULLSTIMER statistics. The following output shows an example of the STIMER output in the SAS log in a UNIX operating environment.

Sample Results of Using the STIMER Option in a UNIX Operating Environment

   NOTE: DATA statement used:
         real time           1.16 seconds
         cpu time            0.09 seconds

Operating Environment Information: See the documentation for your operating environment for information about how STIMER differs from FULLSTIMER in your operating environment. The information that these options display varies depending on your operating environment, so statistics that you see might differ from the ones shown. [cautionend]

Interpreting FULLSTIMER and STIMER Statistics

Several types of resource usage statistics are reported by the STIMER and FULLSTIMER options, including real time (elapsed time) and CPU time. Real time represents the clock time it took to execute a job or step; it is heavily dependent on the capacity of the system and the current load. As more users share a particular resource, less of that resource is available to you. CPU time represents the actual processing time required by the CPU to execute the job, exclusive of capacity and load factors. If you must wait longer for a resource, your CPU time will not increase, but your real time will increase. It is not advisable to use real time as the only criterion for the efficiency of your program because you cannot always control the capacity and load demands on your system. A more accurate assessment of system performance is CPU time, which decreases more predictably as you modify your program to become more efficient.

The statistics reported by FULLSTIMER relate to the three critical computer resources: I/O, memory, and CPU time. Under many circumstances, reducing the use of any of these three resources usually results in better throughput of a particular job and a reduction of real time used. However, there are exceptions, as described in the following sections.

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