Sybase 12.4.2 manual 478

Avoiding buffer manager thrashing

0 0	0	3312376	31840	0	8	0	0	0	0	0	0	0	0	297	201	472	82	4	14
0 0	0	3312376	31484	2	3	0	0	0	0	0	0	0	0	260	169	597	80	3	17
0 0	0	3312368	31116	0	8	0	0	0	0	0	0	0	0	205	1202	396	67	4	29

The above output shows a steady Adaptive Server IQ querying state where the physical memory of the machine has not been overallocated. Little to no system page faulting is occurring. These next set of examples show vmstat output that indicates a problem. (The output shown omits some of the above fields to fit better on the page.)

procs		memory				page					faults			cpu
r b w swap			free	re	mf	pi po fr de sr					in	sy	cs us sy			id
0 0	0	217348	272784	0	148	11	3	9	0	2	251	1835	601	6	3	91
0 0	0	3487124	205572	0	5	0	0	0	0	0	86	131	133	0	1	99
0 0	0	3487124	205572	0	5	0	0	0	0	0	71	162	121	0	0	100
0 0	0	3483912	204500	0	425	36	0	0	0	0	169	642	355	2	2	96
0 0	0	3482740	203372	0	17	6	0	0	0	0	158	370	210	1	3	97
0 0	0	3482676	203300	0	4	10	0	0	0	0	160	1344	225	1	2	97
0 0	0	3343272	199964	1	2123	36	0	0	0	0	213	131	399	7	8	85
0 0	0	3343264	185096	0	194	84	0	0	0	0	283	796	732	1	6	93
0 0	0	3342988	183972	0	17	58	0	0	0	0	276	1051	746	2	4	94
0 0	0	3342860	183632	0	119	314	0	0	0	0	203	1660	529	3	4	94
0 0	0	3342748	182316	2	109	184	0	0	0	0	187	620	488	4	2	95
0 0	0	3342312	181104	2	147	96	0	0	0	0	115	256	260	9	2	89
0 0	0	3340748	179180	0	899	26	0	0	0	0	163	836	531	4	4	92
0 0	0	3328704	167224	0	2993	6	0	0	0	0	82	2195	222	4	7	89

The first line of the above output provides a summary of the system activity since the machine was started. The first three lines show that there is approximately 200MB of free physical memory and that the machine is idle. The fourth line corresponds to Adaptive Server IQ starting up for the first time. Beginning at the eighth line, the amount of free memory starts to reduce rapidly. This corresponds to the Adaptive Server IQ buffer caches being allocated and database pages being read in from disk (note that CPU usage has increased). At this time there is little user CPU time as no queries have begun.

procs		memory				page					faults			cpu
r b	w swap		free	re	mf	pi	po	fr	de	sr	in	sy	cs	us sy id
7 0	0	3247636	58920	0	1880	1664	0	0	0	0	1131	442	1668	80	18	3
18 0	0	3246568	43732	0	709	1696	0	0	0	0	1084	223	1308	90	10	1
12 0	0	3246604	37004	0	358	656	0	0	0	0	600	236	722	95	5	0
15 0	0	3246628	32156	0	356	1606	0	0	0	0	1141	226	1317	91	9	0

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