buffers.g Command

For Windows: Not Supported

Used in conjunction with the buffers BASIC program, the buffers.g command produces a graphic histogram of buffer usage for a range of dates and times.

Syntax

buffers.g counter {start.day{-end.day} {step {start.time-{end.time}}} {(options}

Parameter(s)

counter	Attribute name in the dm,buffers.log, file to examine.
start.day	Beginning day-of-the-week for the graph results. The available values are: Sunday–Saturday or 0–6.
end.day	Ending day-of-the-week for the graph results. The available values are: Sunday–Saturday or 0–6.
*	Spans the entire week.
start.time	Beginning time-of-day for the graph results. The valid values are: 00:00:00–23:59:59.
end.time	Ending time-of-day for the graph results. The valid values are: 00:00:00–23:59:59.
options	g	Displays a graph, rather than a histogram. With this option, the step is automatically calculated. The results are averaged in an attempt to make the curve smoother.
	p	Directs output to printer.

The reports are histogram averages of the buffer values sampled over a period of time (from the buffers command). These reports can give the system administrator a better idea of the workload of the D3 system, and identify possible bottlenecks in the system’s performance.

The activity log is stored in the file buffers.log with a data level per weekday (buffer.log, Monday, buffer.log, Tuesday, and so on). The file is created automatically when the buffers command, with the h option, is used for the first time. Each data level is cleared when changing the day, so that the file records a whole week of activity automatically. The item-ID is the internal time.

The buffers command also creates automatically the dictionary attributes corresponding to the various counters, as shown in the next table. The attribute time displays the sampling time and the attribute description, in the D-pointers Monday, Tuesday and so on, contains the date. The file is created with a dx attribute.

The available attribute names include:

0	time	Times.
1	activ	Activations.
2	idle	Idle time.
3	fflt	Frame faults.
4	writes	Disk writes.
5	bfail	Buffer search fails.
6	fqfull	Read queue full.
7	wqfull	Write queue full.
8	dskerr	Disk errors.
9	elapsd	Elapsed time.
21	ww	Write required.
22	iobusy	I/O busy.
23	mlock	Memory locked.
24	ref	Referenced.
25	wq	Enqueued writes (write queues).
26	tophsh	Top-of-hash.
27	avail	Number of available buffers.
28	batch	Batch.

Additional attributes available on a hosted UNIX system include:

10	dblsrc	Double-source.
11	breuse	Buffers reused.
12	bsleep	Buffers sleeping.
13	sem	Semaphores.

Example(s)

buffers.g sem 6

0 1 2 3 4 5 6...

+------+------+------+------+------+------+---

16:52:05

16:52:11

16:52:18 **************

16:52:25

16:52:31

16:52:38 *******

16:52:45 *********************

16:52:51

16:52:58

16:53:05 *******

16:53:12 *******

16:53:18

Number of samples : 13

Total : 14

Average per period : 0.0002 / sec.

Max value : 4

Max value /s : 0.2857

Peak time : 16:52:45

buffers.g writes tuesday (g

49.0 *

46.3 | *

43.5 | * **

40.8 | *** * * ***

38.1 | * *** * ** **

35.4 | * * ** * *** * **

32.7 |* * *** ** *

29.9 | **

27.2 | **

24.5 |

21.8 |

19.0 |

16.3 |

13.6 |

10.9 |

8.2 |

5.4 |

2.7 |

0/s +------+------+------+------+------+------+------

09:09:26 09:11:46 09:14:06 09:16:26

buffers.g fflt * 01:00:00

Lists the number of frames faults (disk reads), for the whole week, by step of one hour. In the example below, no history was recorded before Wednesday.

No log for Sunday

No log for Monday

No log for Tuesday

20Feb2003; Wednesday; Ctr=fflt, Step=01:00:00, Range=00:00:00-23:59:59

0 8848 17696 26544 35392 44240 53088 61936

+------+------+------+------+------+------+------+------+----

10:59:28 *************************

11:59:54 ***********************************************************

13:00:25 **********************************************************

14:00:52 ************************************

15:01:18 ***************************

16:01:49 ********************************************************

17:02:22 ***************************************

18:02:55 ******

19:03:32 ***********************************************

20:04:08 *************************************************

21:04:43

22:05:21 ***************************************************

23:05:55 *************

Number of samples : 155

Total : 622070

Average per period : 7.1999 / sec.

Max value : 88481

Peak time : 13:00:25

buffers.g ww monday-friday 00:30 08:00-17:30 (p

Lists the percentage of write-required buffers, for the weekdays only, during business hours, by steps of 30 minutes.

Interpreting Results

After taking a significant sample, list the results with the buffers.g command. The most useful parameters to survey are:

Fflt	Measures the number of frame faults. If this number approaches the disk bandwidth as determined by the manufacturer, the system becomes disk bound. Solutions range from increasing the memory allocated to D3, to changing disks, or reorganizing the D3 database on separate disks to increase parallelism.
Writes	Number should stay about one third to a half of the number of frame faults. It is not normal for a system to do more writes than it reads, under normal operation.
Bfail	Number should never be nonzero. If it is not the case, the memory allocated to D3 is definitely too small.
WqFull	Number should not be nonzero too often. If it is the case, and if the number of writes is too big also, there is an abnormal rate of writes.
Bcolls	If this number becomes too high, this indicates that a lot of batch jobs (for example, selects of big files) are done while other processes are doing data entry. It is also an indicator that indeed interactive jobs are receiving higher priority than batch processes.
ww	Number should never go above 50% of the whole buffer pool. If this is the case, the flusher is probably not activated often enough.
avail	Number should never go below 10% of the whole buffer pool. If this is the case, memory must be increased or the flusher must be adjusted.