Displays activity information about the database buffer cache (also called the buffer pool). There are three sets of information: the overall buffer pool, the primary buffer pool, and the Alternate Buffer Pool.

PROMON Buffer Cache Activity display

The following shows a sample Buffer Cache Activity display.

06/30/09        Activity: Buffer Cache
11:35:03        06/30/09 11:23 to 06/30/09 11:33 (9 min 23 sec)

                            Total       Per Min   Per Sec    Per Tx
Database Buffer Pool
Logical reads               28841          3074     51.23      7.14
Logical writes              32703          3485     58.09      8.10
O/S reads                     358            38      0.64      0.09
O/S writes                    748            80      1.33      0.19
Checkpoints                     8             1      0.01      0.00
Marked to checkpoint          525            56      0.93      0.13
Flushed at checkpoint         463            49      0.82      0.11
Writes deferred             32161          3427     57.12      7.97
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:  99 %

Primary Buffer Pool 
Logicalreads                12862          1371     22.85      3.19
Logical writes              18306          1951     32.52      4.53
O/S reads                      10            11     0.18       0.03
O/S writes                    310            33     0.55       0.08
Marked to checkpoint           25             3     0.04       0.01
Flushed at checkpoint          25             3     0.04       0.01
Writes deferred             18279          1948    32.47       4.53
LRU skips                       0             0     0.00       0.00
LRU writes                      0             0     0.00       0.00
APW enqueue                     0             0     0.00       0.00
Primary buffer pool hit ratio:  99 %

Alternate Buffer Pool
Logical reads              15979          1703     28.38       3.96
Logical writes             14397          1534     25.57       3.57
O/S reads                    256            27      0.45       0.06
O/S writes                   438            47      0.78       0.11
Marked to checkpoint         500            53      0.89       0.12
Flushed at checkpoint        438            47      0.78       0.11
Writes deferred            13882          1479     24.66       3.44
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:  99 %
LRU swaps                      0             0      0.00       0.00
LRU2 replacment policy disabled.

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.