Release 10.1A: OpenEdge Data Management:
Database Administration

Buffer Cache

Displays activity information about the database buffer cache (also called the buffer pool). Figure 19–33 shows a sample Buffer Cache Activity display.

09/25/03               Activity: Buffer Cache 16:28                  from 09/25/03 13:56 to 09/25/03 13:57 (19 sec)                           Total       Per Min      Per Sec     Per Tx Logical Reads             23          73           1.21        0.00 Logical Writes            0           0            0.00        0.00 O/S reads                 8           25           0.42        0.00 O/S writes                2           6            0.10        0.00 Checkpoints               0           0            0.00        0.00 Marked at checkpoint      0           0            0.00        0.00 Flushed at checkpoint     0           0            0.00        0.00 Writes deferred           0           0            0.00        0.00 LRU skips                 0           0            0.00        0.00 LRU writes                0           0            0.00        0.00 APW Enqueues              0           0            0.00        0.00 Hit Ratio: 68 %

Figure 19–33: PROMON Buffer Cache Activity display

The display lists the following types of buffer cache requests:

Logical Reads — The number of client requests for database block read operations.
Logical Writes — The number of client requests for database block write operations.
O/S reads — The number of database blocks read from disk.
O/S writes — The number of database block writes to disk.
Checkpoints — The number of checkpoint operations.
Marked at checkpoint — The number of blocks scheduled to be written before the end of a checkpoint.
Flushed at checkpoint — The number of blocks that were not written during the checkpoint and that had to be written all at once at the end of the checkpoint.
Writes deferred — The total number of changes to blocks that occurred before the blocks were written. Each deferred write is potentially an I/O operation saved.
LRU skips — The number of times a buffer on the LRU chain was skipped because it was locked or modified.
LRU writes — The number of blocks written to free a buffer for a read operation.
APW Enqueues — The number of modified buffers placed on the APW queue for writing.
Hit Ratio — The percentage of buffer cache requests that did not require a physical disk I/O operation.