Re: Adding more memory = hugh cpu load

Em 10-10-2011 11:04, Shaun Thomas wrote:
> That's not entirely surprising. The problem with having lots of memory
> is... that you have lots of memory. The operating system likes to cache,
> and this includes writes. Normally this isn't a problem, but with 48GB
> of RAM, the defaults (for CentOS 5.5 in particular) are to use up to 40%
> of that to cache writes.

Hi Shawn and all,

After change the parameters in sysctl.conf, during some time I see that
load average downs. But the system loads grow again.

Dirty memory in meminfo is about 150MB and Whriteback is mostly 0 kB.

I drop checkpoint_timeout to 1min and turn on log_checkpoint:

<2011-10-10 14:18:48 BRT >LOG:  checkpoint complete: wrote 6885 buffers
(1.1%); 0 transaction log file(s) added, 0 removed, 1 recycled;
write=29.862 s, sync=28.466 s, total=58.651 s
<2011-10-10 14:18:50 BRT >LOG:  checkpoint starting: time
<2011-10-10 14:19:40 BRT >LOG:  checkpoint complete: wrote 6415 buffers
(1.0%); 0 transaction log file(s) added, 0 removed, 1 recycled;
write=29.981 s, sync=19.960 s, total=50.111 s
<2011-10-10 14:19:50 BRT >LOG:  checkpoint starting: time
<2011-10-10 14:20:45 BRT >LOG:  checkpoint complete: wrote 6903 buffers
(1.1%); 0 transaction log file(s) added, 0 removed, 1 recycled;
write=29.653 s, sync=25.504 s, total=55.477 s
<2011-10-10 14:20:50 BRT >LOG:  checkpoint starting: time
<2011-10-10 14:21:45 BRT >LOG:  checkpoint complete: wrote 7231 buffers
(1.1%); 0 transaction log file(s) added, 0 removed, 2 recycled;
write=29.911 s, sync=24.899 s, total=55.037 s
<2011-10-10 14:21:50 BRT >LOG:  checkpoint starting: time
<2011-10-10 14:22:45 BRT >LOG:  checkpoint complete: wrote 6569 buffers
(1.0%); 0 transaction log file(s) added, 0 removed, 1 recycled;
write=29.947 s, sync=25.303 s, total=55.342 s
<2011-10-10 14:22:50 BRT >LOG:  checkpoint starting: time
<2011-10-10 14:23:44 BRT >LOG:  checkpoint complete: wrote 5711 buffers
(0.9%); 0 transaction log file(s) added, 0 removed, 1 recycled;
write=30.036 s, sync=24.299 s, total=54.507 s
<2011-10-10 14:23:50 BRT >LOG:  checkpoint starting: time
<2011-10-10 14:24:50 BRT >LOG:  checkpoint complete: wrote 6744 buffers
(1.0%); 0 transaction log file(s) added, 0 removed, 2 recycled;
write=29.946 s, sync=29.792 s, total=60.223 s
<2011-10-10 14:24:50 BRT >LOG:  checkpoint starting: time

[root@servernew data]# vmstat 1 30 -w
procs -------------------memory------------------ ---swap-- -----io----
--system-- -----cpu-------
  r  b       swpd       free       buff      cache   si   so    bi    bo
   in   cs  us sy  id wa st
22  0       2696    8290280     117852   38431540    0    0   328    59
    9   17  17  3  79  1  0
34  0       2696    8289288     117852   38432268    0    0     8  2757
2502 4148  80 20   0  0  0
39  1       2696    8286128     117852   38432348    0    0    24   622
2449 4008  80 20   0  0  0
41  0       2696    8291100     117852   38433792    0    0    64   553
2487 3419  83 17   0  0  0
42  1       2696    8293596     117852   38434556    0    0   232   776
2372 2779  83 17   0  0  0
44  1       2696    8291984     117852   38435252    0    0    56   408
2388 3012  82 18   0  0  0
26  0       2696    8289884     117856   38435924    0    0    64   698
2486 3283  83 17   0  0  0
31  0       2696    8286788     117856   38437052    0    0    88   664
2452 3385  82 18   0  0  0
42  0       2696    8284500     117868   38437516    0    0   176   804
2492 3876  83 17   0  0  0
44  0       2696    8281392     117868   38438860    0    0    24   504
2338 2916  80 20   0  0  0
44  0       2696    8278540     117868   38439152    0    0    32   568
2337 2937  83 17   0  0  0
45  0       2696    8280280     117868   38440348    0    0    72   402
2492 3635  84 16   0  0  0
35  2       2696    8279928     117868   38440388    0    0   184   600
2492 3835  84 16   0  0  0
41  0       2696    8275948     117872   38441712    0    0   136   620
2624 4187  79 21   0  0  0
37  0       2696    8274392     117872   38442372    0    0    24   640
2492 3824  84 16   0  0  0
40  0       2696    8268548     117872   38443120    0    0     0   624
2421 3584  81 19   0  0  0
32  0       2696    8268308     117872   38443652    0    0    16   328
2384 3767  81 19   0  0  0
38  0       2696    8281820     117872   38427472    0    0    72   344
2505 3810  81 19   0  0  0
41  0       2696    8279776     117872   38427976    0    0    16   220
2496 3428  84 16   0  0  0
27  0       2696    8283252     117872   38428508    0    0   112   312
2563 4279  81 19   0  0  0
36  0       2696    8280332     117872   38429288    0    0    48   544
2626 4406  80 20   0  0  0
30  0       2696    8274372     117872   38429372    0    0    24   472
2442 3646  80 19   0  0  0
38  0       2696    8272144     117872   38429956    0    0   152   256
2465 4039  83 16   0  0  0
41  2       2696    8266496     117872   38430324    0    0    56   304
2414 3206  82 18   0  0  0
32  0       2696    8267188     117872   38431068    0    0    64   248
2540 4211  78 22   0  0  0
37  0       2696    8278876     117872   38431324    0    0    56   264
2547 4523  81 19   0  0  0
43  1       2696    8277460     117872   38431588    0    0    40  8627
2695 4143  82 18   0  0  0
41  0       2696    8272556     117872   38431716    0    0    40   216
2495 3744  79 21   0  0  0
40  1       2696    8267292     117876   38433204    0    0   192   544
2586 4437  77 23   0  0  0
34  1       2696    8263204     117876   38433628    0    0   320   929
2841 5166  78 22   0  0  0

Notice that we have no idle % in cpu column.

[root@servernew data]# uptime
  14:26:47 up 2 days,  3:26,  4 users,  load average: 48.61, 46.12, 40.47

My client wants to remove the extra memory... :/

Best regards.