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Avoiding buffer manager thrashing
478
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