SAR (Context Switch)

To monitor the context switching activity

# sar -wP ALL 10 5

Context switching happens when a multi-process OS suspends running one process or thread and starts another. Context switching occurs during any of the following,

• A time slice expires.
• A process exits
• A process puts itself to sleep or in a stopped state.
• A real-time priority process becomes ready to run.

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SAR (Paging)

To monitor paging activity

# sar -r 10 5

The o/p has the following columns

Slots - No. of free pages (4kb pagesize) available. (672979 *4*1024) kb.
Cycle/s- No. of page replacement cycles per second.
Fault/s - No. of page faults per second.
Odio/s - No. of non-paging disk I/O per second.

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SAR (System Buffer Usage)

To monitor the system's buffer activity (not Oracle's buffer cache).

# sar -b 10 5

It provides the number of transfers per second between system buffers and block devices.

Bread/s, bwrit/s -No. of physical I/O. Gives overall write activity on server.
Lread/s, lwrit/s -No. of reads and writes from and to system’s buffer cache.
Pread/s, pwrit/s -No. of I/O on raw devices.
%rcache, %wcache-Buffer cache hit ratio for read and write requests. (100* (lread –bread)/lread )

Inference

• %rcache > 90% indicates the potential for bad disk I/O.
• %wcache < 70% indicates the potential for bad disk I/O.

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SAR (IO)

To monitor the disk usage

# sar -d 10 5

The o/p has the following columns

%busy- The portion of time the device was busy servicing a transfer request.
avque - The average number of requests in queue.
r+w/s- Number of read and write requests per second.
Kbs/s - The number of Kbytes transferred per second.
avwait- The average time each request waits in the queue before it is serviced.
avserv- The average time taken for servicing a request.

Inference

• %busy > 50 on a device indicates contention.
• Avwait should not be greater than avserv
• A high %busy and high avque indicates a big I/O bottleneck.

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SAR (Cpu) Individual

To monitor one CPU at a time.

# sar -P 2 10 5

The o/p displays the result for the 3rd CPU, 10 seconds apart, 5 times.

# sar -P 0,3 10 5

The o/p displays the result for the 1st and 4th CPU, 10 seconds apart, 5 times.

# sar -P ALL 10 5

The o/p displays the result for all the CPU, 10 seconds apart, 5 times.

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SAR (Cpu)

To monitor CPU usage

# sar -u 10 5

The o/p has the following columns.

%usr - Percent of CPU running in user mode (executing user code).
%sys - Percent of CPU running in system mode (executing OS code).
%wio - Percent of CPU running idle with a process waiting for block I/O.
%idle - Percent of CPU that is idle.

Inference

• A low %idle indicates CPU intensive job.
• A high %wio indicates a disk contention.
• A high %sys (>20) indicates a bottleneck. May be due to swapping or paging.
• A high %usr indicates applications not tuned properly or over utilization of CPU.

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