Displays activity information about the following database buffer cache (also called the buffer pools):
  • Database buffer pool
  • Primary buffer pool
  • Alternate buffer pool
  • Private buffer pool

PROMON Buffer Cache Activity display

The following shows a sample Buffer Cache Activity display.

05/03/23        Activity: Buffer Cache
09:07:28        05/03/23 09:05 to 05/03/23 09:07 (2 min 1 sec)
                  
Total         Per Min          Per Sec          Per Tx
                  
Database Buffer Pool
Logical reads                      213555          105895          1764.92            0.00
Logical writes                          0               0             0.00            0.00
O/S reads                          100117           49645           827.41            0.00
O/S writes                              3               1             0.02            0.00
Checkpoints                             0               0             0.00            0.00
Marked to 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
Database buffer pool hit ratio:  53 %

                  
Primary Buffer Pool
Logical reads                       42356           21003           350.05            0.00
Logical writes                          0               0             0.00            0.00
O/S reads                            1085             538             8.97            0.00
O/S writes                              3               1             0.02            0.00
Marked to 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
Primary buffer pool hit ratio:  97 %

                  
Alternate Buffer Pool
Logical reads                           0               0             0.00            0.00
Logical writes                          0               0             0.00            0.00
O/S reads                               0               0             0.00            0.00
O/S writes                              0               0             0.00            0.00
Marked to checkpoint                    0               0             0.00            0.00
Flushed at checkpoint                   0               0             0.00            0.00
Writes deferred                         0               0             0.00            0.00
LRU2 skips                              0               0             0.00            0.00
LRU2 writes                             0               0             0.00            0.00
APW enqueues                            0               0             0.00            0.00
Alternate buffer pool hit ratio:   0 %
LRU2 replacement policy disabled.

                  
Private Buffer Pool
Logical reads                      171199           84892          1414.87            0.00
O/S reads                           99032           49107           818.45            0.00
Private buffer pool hit ratio:  42 %

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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.