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Full Discussion: Memory usage in AIX server
Operating Systems AIX Memory usage in AIX server Post 302843520 by MichaelFelt on Tuesday 13th of August 2013 03:25:07 PM
Old 08-13-2013
The first thing I look at, for a feeling of how the system has been behaving since boot is vmstat -s
michael@x054:[/home/michael]vmstat -s
Code:
            158133157 total address trans. faults
              1263956 page ins
              3733162 page outs
                    0 paging space page ins
                    0 paging space page outs
                    0 total reclaims
             68833738 zero filled pages faults
                92593 executable filled pages faults
                    0 pages examined by clock
                    0 revolutions of the clock hand
                    0 pages freed by the clock
              3246161 backtracks
                    0 free frame waits
                    0 extend XPT waits
              1009416 pending I/O waits
              3108184 start I/Os
              1608563 iodones
            184504298 cpu context switches
             23924465 device interrupts
               431099 software interrupts
             97864862 decrementer interrupts
                    0 mpc-sent interrupts
                    0 mpc-receive interrupts
                    0 phantom interrupts
                    0 traps
           3552750682 syscalls

Further, I prefer the command lsps -s for an accurate view of how much paging space is being used.
Code:
michael@x054:[/home/michael]lsps -s
Total Paging Space   Percent Used
      512MB               3%

My rule of thumb is that paging space percent used should be less than 20%. I start very small (512MB for 9G of memory on my current system) - because I do not want to see paging activity to/from paging space. Everything above what is needed is just being wasted.
And I definitely disagree with multiple paging spaces to "tune" paging space. If you paging space is active - you have an application "condition", generally a configuration issue. If not, add more memory. Tuning paging space was acceptble back when a large system had 128MB-512MB of memory, and less than 4GB disk space. This is today - forget best practice anno 1994 - at least for AIX.

Further, as said above, AIX caches stuff in memory. Generally there are two categories to worry about: file and computational.

Computational is best compared with legacy *nix memory model while file memory is everything else that AIX caches via virtual memory manager. The premise is i/o to/from memory is faster than i/o to/from disk.

So, on an AIX system is quite common to see the total writes (page outs) to be larger than the reads (page ins) - see above - because the data is being written to disk but just stays in memory (cached) and a physical i/o (page in) is not needed when the data is needed later.

Rather than the nmon view, try the topas view
Code:
Topas Monitor for host:    x054                 EVENTS/QUEUES    FILE/TTY
Tue Aug 13 19:23:32 2013   Interval: 10         Cswitch     766  Readch  1818.9K
                                                Syscall    9865  Writech  289.8K
CPU  User%  Kern%  Wait%  Idle%                 Reads      4190  Rawin         0
ALL   27.3    5.9    0.1   66.7                 Writes      177  Ttyout       69
                                                Forks         0  Igets         0
Network  KBPS   I-Pack  O-Pack   KB-In  KB-Out  Execs         1  Namei       309
Total   499.7    175.6   395.3    13.1   486.6  Runqueue    5.2  Dirblk        0
                                                Waitqueue   0.0
Disk    Busy%     KBPS     TPS KB-Read KB-Writ                   MEMORY
Total     0.3     50.4     3.0     0.0    50.4  PAGING           Real,MB    9216
                                                Faults      384  % Comp     36
FileSystem        KBPS     TPS KB-Read KB-Writ  Steals        0  % Noncomp  12
Total              1.6K    3.8K   1.5K  42.1    PgspIn        0  % Client   12
                                                PgspOut       0
Name            PID  CPU%  PgSp Owner           PageIn        0  PAGING SPACE
httpd       7929976  12.1  15.5 httpd           PageOut       9  Size,MB     512
named9      2556034   9.8  28.0 root            Sios          9  % Used      2
mysqld      6226088   8.2  22.3 mysql                            % Free     98
db2sysc     7078126   0.2  25.8 ldapdb2         NFS (calls/sec)
topas_nm    6160612   0.1   2.6 root            SerV2         0  WPAR Activ
topas      11862064   0.1   1.5 michael         CliV2         0  WPAR Total
nfsd        4128958   0.1   0.3 root            SerV3         0  Press: "h"-help
ksh         5636284   0.0   0.5 root            CliV3         0         "q"-quit
gil          720922   0.0   0.1 root
db2fmcd     5505196   0.0   1.1 root

On the right side, under MEMORY, you can see the Computational (Comp) and other/File memory (noncomp) and below that the Paging Space. In the middle is the column Paging.

Depending on how quick I want to see results I set the interval to 5, 15 or 60 seconds (topas -i ##)

Hope this helps with understand what to look for!
 

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