When you read a SAS data set or an external file, I/O is measured when input data is copied to the buffer in memory and when it is copied from the output buffer to the output data set.

A page is the unit of data transfer between the storage device and memory.

Increasing the page size can speed up execution time by reducing the number of times SAS has to read from or write to the storage medium. You can use the CONTENTS procedure to report the page size and the number of pages.

You can use the BUFSIZE= system option or data set option to control the page size of an output SAS data set. The new buffer size is permanent. After it is specified, it is used whenever the data set is processed.

You can use the BUFNO= system or data set option to control how many buffers are available for reading or writing a SAS data set. By increasing the number of buffers, you can control how many pages of data are loaded into memory with each I/O transfer.

The product of BUFNO= and BUFSIZE=, rather than the specific value of either option, determines how much data can be transferred in one I/O operation. Increasing either option increases the amount of data that can be transferred in one I/O operation. However, the improvement in I/O comes at the cost of increased memory consumption.

Another way to improve performance is to use the SASFILE statement to hold a SAS data file in memory so that the data is available to multiple program steps. Keeping the data set open reduces I/O processing and open/close operations, including the allocation and freeing of memory for buffers.

When the SASFILE statement executes, SAS allocates the number of buffers based on the number of pages for the data file and index file. If the file in memory increases in size during processing because of changes or additions to the data, the number of buffers also increases.

I/O processing is reduced only if there is sufficient real memory. If SAS uses virtual memory, there can be a degradation in performance.

The IBUFSIZE= system option specifies the page size for an index file. Typically, you do not need to specify an index page size. However, you might need to use the IBUFSIZE= option if the following apply:

The main resource that is saved when reducing levels in the index is I/O. If your application is experiencing a lot of I/O in the index file, increasing the page size might help. However, you must re-create the index file after increasing the page size. The number of pages that are required for the index varies with the page size, the length of the index value, and the values themselves.