1. Chapter 19: Introduction to Efficient SAS Programming
STAT 541
Chapter 19: Introduction to Efficient SAS Programming
©Spring 2012 Imelda Go, John Grego, Jennifer Lasecki and the University of South Carolina

2. SAS System Options to Track Resources
We have already used STIMER
CPU Time and Real Time
FULLSTIMER tracks additional resources (though perhaps not as many as listed here)
I/O swaps
Number of buffers
Buffer size
Memory

3. SAS System Options to Track Resources
My system’s output from FULLSTIMER:
NOTE: PROCEDURE SORT used (Total process time):     
real time           0.04 seconds     
user cpu time       0.00 seconds     
system cpu time     0.00 seconds     
Memory                            88k     
OS Memory                         10920k     
Timestamp            4/16/2012  11:26:43 AM

4. SAS System Options to Track Resources
Typical considerations
Real time/CPU time
Increasing buffer size/# of pages vs. Memory
Decreasing I/O vs. Memory 4

5. Benchmarking The chapters that follow will use benchmarking to study
Memory Usage
Data Storage Space
Best Practices
Efficient Sorting 5

6. Benchmarking
SAS uses data sets of various sizes from SASUSER for benchmarking on a variety of straightforward tasks
Benchmarking guidelines are detailed
Include only essential code
Replication
Realistic conditions 6

7. Chapter 20: Controlling Memory Usage
STAT 541
Chapter 20: Controlling Memory Usage
©Spring 2012 Imelda Go, John Grego, Jennifer Lasecki and the University of South Carolina 7

8. Page Size and Buffers
SAS copies data a “page” at a time to a buffer in memory
Observations are loaded into the PDV (Program Data Vector) one at a time, processed, then read to an output buffer
When the output buffer is full, its contents are written to an output SAS data set.
I/O is measured when input data is copied to the input buffer and when output buffer contents are written to the external data set. 8

9. Page Size and Buffers
We could reduce the number of I/O operations (or swaps) by increasing the page (or buffer) size, or by increasing the number of buffers (some systems allow only a single buffer)
PROC CONTENTS can print the page size
Use BUFSIZE and BUFNO options to change the page size and # of buffers
Obviously, such changes should not be made without an understanding of system defaults etc 9

10. Page Size and Buffers Example proc contents data=stat541.meddb; run;
data meddb;
set stat541.meddb;
data meddb (bufsize=6144 bufno=2); 10

11. SASFILE The SASFILE statement holds the data set in memory.
Useful when
The data will be used for multiple data/proc steps
Sufficient real memory is available
A part of the data can be processed separately
Be aware of unintended consequences when not enough memory is available. 11