A buffer hit occurs when the database engine locates a record in the buffer pool and does not have to read the record from disk. See Database buffers for an explanation of buffer hits and how they improve performance by reducing overhead. When tuned correctly, the engine should achieve a buffer hit most of the time.

To determine the efficiency of database buffer activity, check the Buffer Hits field of the PROMON Activity option. For best performance, increase the Blocks in Database Buffers (-B) parameter until the buffer hits percentage exceeds 95 percent, or until your system starts paging. The following figure shows the Buffer Hits field in a sample Activity display.

Figure 1. Monitoring buffer activity