SAS Chapter 20: Controlling Memory Usage

1. The total number of bytes occupied by a data set equals…?

The page size multiplied by the number of pages.

The page size multiplied by the number of observations.

The sum of the page size and the number of pages.

The number of pages multiplied by the number of variables.

The total number of bytes occupied by a data set equals the page size multiplied by the number of pages. You can use the CONTENTS procedure to report the page size and the number of pages.

Explanation

The total number of bytes occupied by a data set equals the page size multiplied by the number of pages. You can use the CONTENTS procedure to report the page size and the number of pages.

2. Which of the following statements is true regarding a file that is opened with the SASFILE statement?

The file is available to subsequent DATA and PROC steps or applications until a SASFILE END statement is executed.

The file is available for subsequent utility or output processing until the program ends.

If the file increases in size during processing, the number of buffers remains the same.

When a SAS data file is opened using the SASFILE statement, the data is held in memory, and is available to subsequent DATA and PROC steps or applications, until either a SASFILE CLOSE statement is executed or the program ends. Though a file that is opened with the SASFILE statement can be used for subsequent input or update processing, it cannot be used for subsequent utility or output processing. If the file in memory increases in size during processing, the number of buffers also increases.

Explanation

When a SAS data file is opened using the SASFILE statement, the data is held in memory, and is available to subsequent DATA and PROC steps or applications, until either a SASFILE CLOSE statement is executed or the program ends. Though a file that is opened with the SASFILE statement can be used for subsequent input or update processing, it cannot be used for subsequent utility or output processing. If the file in memory increases in size during processing, the number of buffers also increases.

3. Which statement opens the file Work.Quarter1, allocates enough buffers to hold the entire file in memory, and reads the data into memory?

Sasfile work.quarter1 open;

Sasfile work.quarter1 load;

Sasfile work.quarter1 bufno=max;

Sasfile work.quarter1 bufsize=max;

The SASFILE LOAD statement opens the file, allocates the buffers, and reads the data into memory.

Explanation

The SASFILE LOAD statement opens the file, allocates the buffers, and reads the data into memory.

4. Which of the following statements is true regarding the BUFNO= option?

The BUFNO= option specifies the size of each buffer that is used for reading or writing a SAS data set.

The BUFNO= option can improve execution time by limiting the number of input/output operations that are required.

Using the BUFNO= option results in permanent changes to the data set.

Using the BUFNO= option to increase the number of buffers results in decreased memory consumption.

You can use the BUFNO= system option or data set option to control how many buffers are available for reading or writing a SAS data set. Using BUFNO= can improve execution time by limiting the number of input/output operations that are required for a particular SAS data set. However, the improvement in I/O comes at the cost of increased memory consumption. The buffer number is not a permanent attribute of the data set and is valid only for the current step or SAS session.

Explanation

You can use the BUFNO= system option or data set option to control how many buffers are available for reading or writing a SAS data set. Using BUFNO= can improve execution time by limiting the number of input/output operations that are required for a particular SAS data set. However, the improvement in I/O comes at the cost of increased memory consumption. The buffer number is not a permanent attribute of the data set and is valid only for the current step or SAS session.

5. Which of the following statements is not true regarding a page?

A page is the unit of data transfer between the engine and the operating environment.

A page includes the number of bytes used by the descriptor portion, the data values, and the overhead.

The size of a page is analogous to buffer size.

The size of a page can be changed at any time.

A page is fixed in size when the data set is created, either to a default value or a specified value. You can use the BUFSIZE= option to control the page size of an output SAS data set. BUFSIZE= specifies not only the page size (in bytes), but also the size of each buffer that is used for reading or writing the SAS data set. The new buffer size is permanent; after it is specified, it is used whenever the data set is processed.

Explanation

A page is fixed in size when the data set is created, either to a default value or a specified value. You can use the BUFSIZE= option to control the page size of an output SAS data set. BUFSIZE= specifies not only the page size (in bytes), but also the size of each buffer that is used for reading or writing the SAS data set. The new buffer size is permanent; after it is specified, it is used whenever the data set is processed.