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 Buffer Monitor and Tune SummaryLocate this document in the navigation structure

To call the buffer monitor:

Choose the following path in the SAP Easy Access menu: Administration →CCMS →Control/Monitoring →Performance →Setup/Buffers →Buffers, or call transaction ST02.

The buffer monitor displays information about buffer and memory usage for the instance where the user is logged on. Statistics are compiled from the time the server is started.

The Tune Summary screen is divided into four parts:

  • Buffer
  • SAP memory
  • Cursor cache
  • Call statistics

Buffer

The first column shows the names of the buffers:

  • Four ABAP repository buffers
  • The program, CUA, screen, and calendar buffers
  • The table buffers

See also:

Repository Buffer (Nametab Buffer)

Hit Ratio

The hit ratios are displayed as percentages.

A hit is when an object (such as a table, screen, or program) in the buffer is accessed. If the object has to be read from the database, the buffer access fails.

Buffer hit ratio = buffer object reads/logical requests

Buffer Quality

Buffer Quality = saved database calls / (database calls + saved database calls)

The database interface can translate one logical request into several database calls.

Buffer Quality

Allocated Size

The allocated size is measured in KB. It is different from the available buffer size because a part of the size is used for buffer management.

Freespace 

Freespace is important for analyzing the buffer size. The space remaining in the buffer is displayed in KB and percentage of the available buffer size.

Number of Directories

Even though there is freespace in the buffer, objects may not always be loaded into the buffer because there are no more free directories. The Buffers Monitor displays the number of directories available for the buffer, and the number and percentage free. The buffer directories point to the location of the objects that are located in the buffer.

Swapping

When a buffer has insufficient freespace or free directories, it has to swap objects out of the buffer in order to load a new object. The column Swap shows how many objects have been swapped out since system startup.

Database Accesses

When an object cannot be read from the buffer, the database has to be accessed. The number of database accesses is displayed in the last column of this screen.

Note

If a critical situation occurs in a buffer, the data for that buffer (freespace/object swaps) is displayed in red.

SAP Memory

The following information is displayed:

  • The amount of space currently used as a percentage and in KB
  • The maximum value (max. use) since system startup
  • The amount of space used in shared memory and on the disk

See also:

Roll and Paging Buffers

For more information:

If you require detailed information on an individual memory area, select a line.

In the Detailed Analysis windows (Extended Memory and Heap Memory) include functions that provide information about:

  • Quotas

    Memory allocation (sequence, size)

  • Ext. mem. blocks

    Extended memory user

  • Current parameters

    The instance profile settings for memory management

  • History

    Memory usage over the course of several days.

SAP Cursor Cache

The SAP system has a cursor cache that stores cursors for SELECT statements to avoid time consuming PREPARE processing.

Note

This cache has a fixed size and cannot be tuned.

 

SAP Cursor Cache

Call Statistics

The Tune Summary screen displays the access statistics for all data either residing in the SAP pool buffers or the database.

The following table describes the information of the tune summary.

Table: Tune Summary

Screen

Information

First column

Contains the different kinds of statements that can be used to access a table.

(SELECT SINGLE, SELECT, INSERT, UPDATE, DELETE).

Last line

Shows the total - or in the case of the hit ratios, the average - data of the call statistics.

Next column

Shows the hit ratios for the SELECT statements for buffered tables.

A hit ratio for the other statements (UPDATE, INSERT, and DELETE) is not displayed because these statements always have to be passed to the database.

ABAP Processor

Displays the number of logical requests to the buffered tables,

and how many of them failed.

The subsequent columns display:

  • The average database call time
  • The number of affected rows
    Note

    Table access failures are not the same as buffer access fails. The SQL statements SELECT SINGLE, INSERT, DELETE, and UPDATE can fail if the specified data record does not exist. A buffer access can "fail" if the table has not yet been loaded into the buffer.

Some of the logical requests cannot be satisfied by buffer access, and cause database accesses.

Buffer History

Analyze the buffer history to find the correct buffer sizes.

To display the buffer history:

Choose the following path in the SAP Easy Access menu: Administration → CCMS →   Control/Monitoring → Performance → Setup/Buffers → Buffers → Goto → Performance database → This server history.

The data displayed is similar to the columns in the Tune Summary.

The capacities of the buffers may be appropriate for the current system situation. However, you can see that the capacity was too small for recent days. You should resize the buffers even if the situation is not so bad at the moment.

See also:

Checking Memory Usage

Displaying Table Buffers