Use the Buffer Pool window to view important statistics
about an active buffer pool.
To display the Buffer Pool window, select any active buffer pool
listed in the Buffer Manager window.
On the Buffer Pool window, select the required type
of information. A further window then displays the requested information.
Use the scrolling keys F7 (Up) and F8 (Down) to
view the portions of the window not displayed. Figure 1. Buffer
Pool window
DGOMSWBY Buffer Pool BP1
Command ===> _______________________________________________________
For details, type any character next to heading, then press Enter.
_ General
_ Read Operations
_ Write Operations
_ Query Parallelism
_ Sort/Merge Work File Operations
F1=Help F3=Exit F5=Auto F6=History F7=Up
F8=Down F10=Delta F11=Interval F12=Cancel F16=Look
F17=Collect
Depending on your selection one of the following windows is displayed.
Each window is followed by a description of some of the important
fields shown in this window. Figure 2. Buffer Pool – General window
The total number of Getpage operations, minus the number of pages
read from a hard disk drive (both synchronously and using Prefetch),
divided by the total number of Getpage operations, multiplied by 100.
Current active buffers
Total number of current active (nonstealable) buffers at the moment
the statistics were collected. A buffer critical condition is only
shown if it occurs at that moment. The buffer pool might be too small
if the number of active buffers is greater than the Deferred Write
threshold (DWQT) of the buffer pool.
The number of Getpage requests issued by sequential
and random requests.
Synchronous reads - Total
The number of synchronous read I/O operations performed by sequential
and random requests.
Sequential prefetch - Reads
The number of times Sequential Prefetch reads were performed.
Sequential prefetch - Pages read
Number of pages read because of Sequential Prefetch.
The ratio
of Sequential prefetch - Pages read to Sequential
prefetch - Reads is between 0 and 32. Normally 32 is the
maximum Prefetch quantity for table space scans, whether data or index.
List prefetch - Reads
Number of times List Prefetch reads were performed.
List prefetch - Pages read
Number of pages read because of List Prefetch.
The ratio of List
prefetch - Pages read to List prefetch - Reads is
between 0 and 32.
Dynamic prefetch - Reads
Number of times Dynamic Prefetch reads were performed.
Dynamic prefetch - Pages read
Number of pages read because of Dynamic Prefetch performed because
of sequential detection.
The ratio of Dynamic prefetch
- Pages read to Dynamic prefetch - Reads is
between 0 and 32.
Prefetch disabled - No buffer
Number of times Sequential Prefetch was disabled because buffers
were not available. This is the number of times the Sequential Prefetch
threshold was reached. This fixed threshold is experienced if 90%
of the pages in the buffer pool are unavailable. This has a significant
effect on large and frequent scans that use Sequential Prefetch.
Number of times pages were updated in the buffer pool.
Pages written
Number of pages written. This field contains the number of pages
in the buffer pool written to a hard disk drive.
Synchronous writes
Total number of immediate Writes for a page.
An immediate
Write can occur when:
Data set is closed
DB2® Checkpoint is taken
Immediate Write threshold (97.5% pages in the buffer pool are
unavailable), which is a fixed threshold
a Write engine is not available
Asynchronous writes
Number of asynchronous Write I/O operations performed by media
manager to a direct access storage device.
Thresholds reached - Deferred write
Number of times the Deferred Write threshold was reached. This
threshold is a percentage of the virtual buffer pool that might be
occupied by unavailable pages, including both updated pages and pages
in use.
Thresholds reached - Vertical deferred write
Number of times the Vertical Deferred Write threshold was reached.
This threshold is expressed as a percentage of the virtual buffer
pool that might be occupied by updated pages from a single data set.
When this threshold is reached, Writes are scheduled for that
data set.
Thresholds reached - Data manager critical
Number of times the data manager critical threshold was reached.
This fixed threshold is experienced if 95% of the pages in the buffer
pool are unavailable. This has a significant effect on CPU usage.