Example

 $ iostat -xtc 5 2
                          extended disk statistics       tty         cpu
     disk r/s  w/s Kr/s Kw/s wait actv svc_t  %w  %b  tin tout us sy wt id
     sd0   2.6 3.0 20.7 22.7 0.1  0.2  59.2   6   19   0   84  3  85 11 0
     sd1   4.2 1.0 33.5  8.0 0.0  0.2  47.2   2   23
     sd2   0.0 0.0  0.0  0.0 0.0  0.0   0.0   0    0
     sd3  10.2 1.6 51.4 12.8 0.1  0.3  31.2   3   31
 

     The fields have the following meanings:

      disk    name of the disk
      r/s     reads per second
      w/s     writes per second
      Kr/s    kilobytes read per second
      Kw/s    kilobytes written per second
      wait    average number of transactions waiting for service (Q length)

      actv    average number of transactions  actively  

              being serviced (removed  from  the

 	      queue but not yet
              completed)
      %w      percent of time there are transactions  waiting
              for service (queue non-empty)
      %b      percent of time the disk is busy  (transactions
                  in progress)

Results and Solutions:

The values to look from the iostat output  are:

• Reads/writes  per second (r/s , w/s)
• Percentage busy (%b)
• Service time (svc_t)

If a disk shows consistently high reads/writes along with , the percentage busy (%b) of the disks is greater than 5 percent, and the average service time  (svc_t) is greater than 30 milliseconds, then  one of the following action needs to be taken

1.)Tune the application to use disk i/o more efficiently  by modifying the disk queries and using available cache facilities of application servers .

2.) Spread the file system of the disk on to two or more disk  using disk striping feature of volume manager /disksuite  etc.

3.) Increase the system parameter values for  inode cache  , ufs_ninode ,  which is  Number of inodes to be held in memory. Inodes are cached globally (for UFS), not on a per-file system basis 

4.) Move the file system to another faster disk /controller  or replace existing disk/controller to a faster

     one.

Virtual Memory Statistics ( vmstat )

vmstat -  vmstat reports virtual memory statistics of   process, virtual memory, disk, trap, and CPU activity.

 On multicpu systems , vmstat averages the number of CPUs  into  the  output. For per-process statistics .Without options, vmstat displays a one-line summary  of  the  virtual memory activity since the system was booted.

 syntax:

Basic synctax is vmstat  <options>   interval  count

option - let you specify the type of information needed such as paging  -p , cache   -c ,.interrupt -i  etc.

if no option is specified  information about   process , memory , paging , disk ,interrupts & cpu  is displayed  .

interval  - is time period in seconds between two samples . vmstat   4  will give data at each 4 seconds interval.

count  - is the number of times the data is needed . vmstat 4   5   will give data at 4 seconds interval   5

             times.

 Example

     The following command displays a summary of what the  system
     is doing every five seconds.

     example% vmstat 5

     procs  memory          page             disk      faults        cpu
     r b w swap  free re mf pi p fr de sr s0 s1 s2 s3  in  sy  cs us sy id
     0 0 0 11456 4120 1  41 19 1  3  0  2  0  4  0  0  48 112 130  4 14 82
     0 0 1 10132 4280 0   4 44 0  0  0  0  0 23  0  0 211 230 144  3 35 62
     0 0 1 10132 4616 0   0 20 0  0  0  0  0 19  0  0 150 172 146  3 33 64
     0 0 1 10132 5292 0   0  9 0  0  0  0  0 21  0  0 165 105 130  1 21 78

 The fields of vmstat's display are
     procs
             r     in run queue
             b     blocked for resources I/O, paging etc.
            w     swapped

     memory (in Kbytes)
              swap -  amount  of  swap   space   currently   available               
              free   - size of the free list

     page ( in units per second).
           re    page reclaims -  see  -S  option  for  how  this field is modified.
           mf    minor faults -  see  -S  option  for  how    this field is modified.
           pi    kilobytes paged in
           po    kilobytes paged out
           fr    kilobytes freed
           de    anticipated short-term memory shortfall (Kbytes)
           sr    pages scanned by clock algorithm

     disk  ( operations per second )

           There are  slots for up to four disks, labeled with a single letter and number.

           The letter indicates  the  type  of  disk  (s = SCSI, i = IPI, etc) . The number is 

           the logical unit number.

     faults
            in    (non clock) device interrupts
           sy    system calls
           cs    CPU context switches

     cpu  -   breakdown of percentage usage of CPU  time.  On multiprocessors  this is an a

                verage across all processors.
           us    user time
           sy    system time
           id    idle time
 

Results and Solutions:

A.   CPU issues:

Following columns has to be watched to determine if there is any cpu issue

1. Processes in the run queue (procs r)
2. User time (cpu us)
3. System time (cpu sy)
4. Idle time (cpu id)

     procs      cpu
     r b w    us sy  id
     0 0 0    4  14  82
     0 0 1    3  35  62
     0 0 1    3  33  64
     0 0 1    1  21  78

Problem symptoms:

1.) If the number of processes in run queue (procs r) are consistently greater than the number of CPUs on the system it will slow down system as there are more processes then available CPUs .

2.) if  this number is more than four times the number of available CPUs in the system then system is facing shortage of cpu power and will greatly slow down the processess on the system.

3.) If  the idle time (cpu id) is consistently 0 and if the system time (cpu sy) is double the user time (cpu us)  system is facing shortage of CPU resources.

 

Resolution :

Resolution to these kind of issues involves tuning of application procedures  to make efficient use of cpu  and as a last resort increasing the cpu power or adding more cpu to the system.  

 

 

B.   Memory Issues:

Memory bottlenecks are determined by the scan rate (sr) . The scan rate is the pages scanned by the clock algorithm per second. If the scan rate (sr) is continuously over 200 pages per second then there is a memory shortage.

 

Resolution :

1. Tune the applications & servers to make  efficient use of memory and cache.

2. Increase system memory .

3. Implement priority paging in s in pre solaris 8 versions by adding line "set priority paging=1" in

    /etc/system. Remove this line if upgrading from Solaris 7 to 8 & retaining old /etc/system file.

Network Statistics (netstat)

netstat displays the  contents  of  various  network-related  data structures in  depending on the options selected.

Syntax :

netstat  <option/s>

multiple options can be given at one time.

Options

 -a - displays the state of all sockets.
 -r - shows the system routing tables
 -i - gives statistics on a per-interface basis.
-m - displays information from the network memory buffers. On Solaris, this shows statistics

         forSTREAMS
 -p [proto] - retrieves statistics for the specified protocol
  -s - shows per-protocol statistics. (some implementations allow -ss to remove fileds with a value of 0 (zero) from the display.)
 -D - display the status of DHCP configured interfaces.
-n do not lookup hostnames, display only IP addresses.

-d (with -i) displays dropped packets per interface.

-I [interface] retrieve information about only the specified interface.

-v be verbose

interval  -   number for continuous display of statictics.

Example :

This shows the output on a Solaris machine who's IP address is 192.168.1.11 with a default router at 192.168.1.1

Results and Solutions:

A.) Network availability

The command as above is mostly useful in troubleshooting network accessibility issues . When  outside network is not accessible from a machine check the following

1. if the default router ip  address is correct

2.  you can ping it from your machine.

3. If router address is incorrect  it can be changed  with route add  commnad . See man route  for more info .

route command examples:
$route add default <hostname>

$route add 192.0.2.32  <gateway_name>

If the router address is correct but still you can't ping it  there may be some  network cable /hub/switch problem  and you have to try and eliminate the faulty component .

B.) Network Response

$ netstat -i

This option is used to diagnose the network problems when  the connectivity is there but  it is slow in response .

Values to look at:

• Collisions (Collis)
• Output packets (Opkts)
• Input errors (Ierrs)
• Input packets (Ipkts)

The above values will give information to workout

i.  Network collision rate as follows :

Network collision rate = Output collision counts / Output packets

 Network-wide collision rate greater than 10 percent  will indicate

•  Overloaded network,
•  Poorly configured network,
•  Hardware problems. 

ii.  Input packet error rate as follows :

 Input Packet Error Rate = Ierrs / Ipkts.

If the input error rate is high (over 0.25 percent), the host is dropping packets. Hub/switch cables etc needs to be checked for potential problems.

C.  Network socket &  TCP Cconnection state

Netstat gives important   information about network socket and tcp state . This is very useful in
finding out the open , closed and  waiting network tcp connection .

Network states returned by  netstat are following :

     CLOSED               ----  Closed.  The socket  is  not  being used.
     LISTEN                 ----  Listening for incoming connections.
     SYN_SENT           ----  Actively trying to  establish  connection.
     SYN_RECEIVED  ---- Initial synchronization of the connection under way.
     ESTABLISHED     ----  Connection has been established.
     CLOSE_WAIT      ----  Remote shut down; waiting  for  the socket to close.
     FIN_WAIT_1        ----  Socket closed; shutting  down  connection.
     CLOSING             ----  Closed,   then   remote   shutdown; awaiting acknowledgement.
     LAST_ACK          ----   Remote  shut  down,  then   closed ;awaiting acknowledgement.
     FIN_WAIT_2        ----  Socket closed; waiting for shutdown from remote.
     TIME_WAIT         ----  Wait after close for  remote  shutdown retransmission.
     

 

Example:

 #netstat -a

if  you see a lots of connections in FIN_WAIT state  tcp/ip parameters   have to be tuned  because the

connections  are not being closed and they gets accumulating . After some time system may run out of

resource . TCP parameter can be tuned to define a time out so that connections can be released and

used by new connection.  

 

4. Next Steps :

This  article  tried to cover the performance tuning aspects in unix  .There are not many books available in this subject but I have found some good books which will prove to be helpful in performance management  . These books are available for online buying and you should  relevant books from this selection in your personal or official book collection. 

Following are the list of books  recommended for performance tuning  in unix , solaris , HPUX, AIX ,Linux ,oracle & SAP .

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