Buffer Quality

Definition

You only can decide whether the buffer quality is poor after system startup, when the buffer loading phase is complete.

Once an instance is started, the SAP buffers begin to load. After significant initial activity, the buffer quality is soon greater than 90%. (The single key buffer may take a little longer, depending on system activity.)

To find out the buffers with poor quality, first check the system startup time. When the system is started, all buffers (except the program buffer which has a pre-load) are initially empty. Therefore, all objects that are accessed for the first time have to be read from the database and then loaded into the buffers.

If objects are not yet in the buffer, the hit ratio for the buffer will be low. The hit ratio increases from the time objects are loaded into the buffers. The rate of the increase depends on the workload in the system and is different for each buffer.

The single key buffer generally has the slowest increase in quality. For example, you do not have to worry about a single key buffer with a quality of around 80%, if the other buffer qualities are around 90%.

If buffer quality is poor, you should investigate what is happening to a buffer. However, poor buffer quality is not always due to a real problem. For example, transports into a system can reduce buffer quality. This is different for object swapping