Progress
Database Administration
Guide and Reference
Activity Displays>Buffer Cache
Displays activity information about the database buffer cache (also called the buffer pool). Figure A–23 shows a sample Buffer Cache Activity display.
Figure A–23: 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.
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