SunSolve Internal

Infodoc ID		Synopsis		Date
13482		How to use vmstat to determine performance problems		12 May 1998

Description

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The vmstat command will provide some insight into memory and CPU performance
problems.  It can also show possible I/O problems.

For RAM bottlenecks, the 'sr' or scan rate column should be examined.
Scan rates above 200 are an indication that the system is scanning
through memory looking for pages to free at a high rate.  This indicates
that, as well as inactive pages, active pages might be stolen from
processes.  A high scan rate can cause your system to consume more cpu
resources than it normally would.  

In addition to the 'sr' column, check the 'w' column; it contains runnable 
processes that have been swapped out due to lack of RAM.

For CPU bottlenects, examine the 'r' or run queue column.  A
run queue of greater than 3 processes per CPU is an indication of a busy
system.  There is insufficient CPU power, and jobs are spending an
increasing amount of time in the queue before being assigned to a CPU.
This reduces throughput and increases interactive response time.
If "id" idle time is zero you are exhausting all your cpu resources.

Under the "b" column if there is constantly a number in that column you 
are blocked for I/O.  You can then try to determine what is blocking.  It
is usually disks.  Check mpstat to see if "wt" column has a high number.  
That in conjunction with the vmstat "b" column indicate a system blocked for
disk I/O.  You can then run iostat to see what disks are causing problems.