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topas - computational memory 95% : Any Impact?

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Operating Systems AIX topas - computational memory 95% : Any Impact?
# 8  
Old 02-01-2011
Thank you so much. I understand it now. Here are the outputs of two commands.

Code:
# vmstat -Iwt 2 10

System configuration: lcpu=8 mem=22528MB ent=2.00

   kthr            memory                         page                       faults                 cpu             time
----------- --------------------- ------------------------------------ ------------------ ----------------------- --------
  r   b   p        avm        fre    fi    fo    pi    po    fr     sr    in     sy    cs us sy id wa    pc    ec hr mi se
  6   0   0    5507597      24376    11    11     0     0     0      0   482   9042  3459  7  4 88  0  0.25  12.4 14:05:16
  7   0   0    5507596      24358     1   704     0     0     0      0   783   8209  4026  8 19 72  1  0.58  28.9 14:05:18
  6   0   0    5507632      24260    25    26     0     0     0      0   760   8591  3887 19  4 77  0  0.49  24.3 14:05:20
  6   0   0    5507635      24191    24    35     0     0     0      0   709  17631  3755 13 10 76  0  0.49  24.5 14:05:22
  6   0   0    5507634      24131    19    39     0     0     0      0   726  16594  4079 15 11 74  0  0.54  27.0 14:05:24
  6   0   0    5507636      24050    40    37     0     0     0      0   833  10969  3851 22  5 73  0  0.57  28.5 14:05:26
  5   0   0    5507629      23964    53    59     0     0     0      0   879  11698  4336 17  6 77  0  0.47  23.4 14:05:28
  3   0   0    5507636      23881    29    53     0     0     0      0   764   9547  3834 20  5 76  0  0.51  25.6 14:05:30
 12   0   0    5507637      23776    46    98     0     0     0      0   635 146920  3842 26  8 67  0  0.69  34.3 14:05:32
  5   0   0    5507781      23516    67    97     0     0     0      0  1018  78393  4588 26  7 67  0  0.69  34.5 14:05:34

Code:
# vmstat -s
           2987546854 total address trans. faults
             63021994 page ins
             65838621 page outs
                15661 paging space page ins
               102513 paging space page outs
                    0 total reclaims
           1091749680 zero filled pages faults
             12316257 executable filled pages faults
            751950154 pages examined by clock
                 2213 revolutions of the clock hand
             49701994 pages freed by the clock
             29262304 backtracks
                    0 free frame waits
                    0 extend XPT waits
              3287521 pending I/O waits
            128860618 start I/Os
             74277577 iodones
           5183493194 cpu context switches
            693577055 device interrupts
            187124308 software interrupts
           1128729939 decrementer interrupts
              1336301 mpc-sent interrupts
              1336265 mpc-received interrupts
             52813406 phantom interrupts
                    0 traps
          43653242538 syscalls

Moderator's Comments:
Mod Comment edit by bakunin: Please use CODE-tags for posting terminal output. Thank you.
Last edited by bakunin; 02-02-2011 at 05:23 AM..
# 9  
Old 02-02-2011
I am glad it helped.

from your output below
Quote:
r b p avm fre fi fo pi po fr sr in sy cs us sy id wa pc ec hr mi se
12 0 0 5507637 23776 46 98 0 0 0 0 635 146920 3842 26 8 67 0 0.69 34.3 14:05:32
I can see that you are currently not paging what is good - and no scan to free what is good as well - but 22 GB avm (computational memory) when you only have 22 GB is not that good as every new connection / DB query will probably cause paging.

From your vmstat output ...
Quote:
15661 paging space page ins
102513 paging space page outs
Each of these will definitely cause your system to slow down - so you should try to avoid them. Same recommendations I almost always give: try to mount with noatime option and switch Oracle to SETALL - ideally this frees up some computational memory.

Regards
zxmaus
# 10  
Old 02-02-2011
Thanks a lot zxmaus.

What do you mean by mount with noatime option and switch Oracle to SETALL? I mean the commands for them?

Thanks again!
# 11  
Old 02-02-2011
Hello,

for SETALL ask your DBAs ... its a setting within oracle: filesystemio_options=SETALL - it usually is set to none or async - and should be set from oracle 9 onwards to SETALL.
For noatime - smitty chfs - mountoptions noatime (and for dumps if you have such a filesystem choose noatime,rbrw)

Regards
zxmaus

Kind regards
Nicki
# 12  
Old 02-02-2011
Quote:
Originally Posted by zxmaus
well let me disagree here ... computational memory above 85% is never a good idea
Depending on the exact circumstances this is true in most cases, of course. I was a bit too general in my answer.

@panchpan:

Your vmstat output shows several things. First let's look at the memory situation: The "avm" and "fre" columns are displayed in pages of 4k each. You roughly have 5.5 mio pages available ( 5.5 mio x 4k ~ 22GB ) and of these are ~25k pages (~100MB) not used by the system at all. This might be a bit on the light side as a reserve and - as zxmaus has pointed out - you should watch and monitor the system closely to proactively find out probably bottlenecks. Even if you don't have one you might be close to getting one, as zxmaus has already suggested.

On the other hand your "pi" and "po" columns (page in / page out) are constantly zero, which means there is no paging going on yet. Your "vmstat -s" output shows some paging activity, which should be investigated. Issue the same command over the next days once a day and compare the numbers in it. If they remain constant there is nothing to worry, if they increase then paging is happening somewhere and it will be worth it to find out what causes it.

You might also want to issue "vmstat -v" and watch if there are I/O-buffers lacking. (there are also several threads here discussing exactly this)

The CPU part of your vmstat output shows relatively high idle values (id). "us", "sy", "id" and "wa" are percentage values, depicting the time the CPU(s) spend working on user code (basically programs), system code, idling and waiting (for I/O). High waiting numbers mean there are I/O-bottlenecks, because there would be programs ready to do something, which they cannot do because they cannot read their data. There is no such thing in your output, which is a sign of healthiness in this regard.

Notice the "ec" column: this is also a percentage value and signifies the "entitled [CPU] capacity consumed". Your system is allowed to use 2 CPUs and of these about 25% on average (0.5 CPUs) is used. If this value is constantly below 50% you might want to reduce the entitlement to 1 CPU, if it constantly nears 100% you might want to add a CPU to the LPAR configuration. But before suggesting something in this direction first monitor closely over a longer time. There is no sense in doing performance optimization from a single seconds-long snapshot.


I hope these tips help.

bakunin
# 13  
Old 02-02-2011
Nice explanation
The piece by ZXMAUS is one of the best explanations of comp / non-comp memory on AIX I have ever seen.
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