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RE: [nv-l] Status Polling myth

To: nv-l@lists.us.ibm.com
Subject: RE: [nv-l] Status Polling myth
From: Leslie Clark <lclark@us.ibm.com>
Date: Mon, 27 Jun 2005 12:17:05 -0400
Delivery-date: Mon, 27 Jun 2005 17:17:43 +0100
Envelope-to: nv-l-archive@lists.skills-1st.co.uk
In-reply-to: <1D99739B79BF7744BF8927B8F2274CA2063EAF@HQGTNEX5.doe.local>
Reply-to: nv-l@lists.us.ibm.com
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The behavior you are referring to was corrected some time ago. There have been two
changes. In '97, the man man page for ovsnmp.conf was updated to match the actual
behavior, which was NOT exponential increments, but something more arcane as described
in the APAR below. That behavior (decrementing!) I remember as resulting in a lot of
false alarms that appeared to make no sense. That behavior was modified in V6.0.1
to just do what you told it to do. However, the man page for ovsnmp.conf still talks
about increments and decrements. Time for another update...

(What increment exponentially, as I recall, is name resolution timeouts with retries.)

Here's the current behavior, from the release notes for 6.0.1, in the new features section:

Ping and SNMP Timeout Values
The netmon daemon no longer dynamically adjusts the ping and
SNMP timeout values. These values remain as configured in the
SNMP Options dialog.

And here's the description of the apar that tells how it was behaving before that:

APAR - IX68241

The man page for ovsnmp.conf describes the timeoutInterval for  
polling a device.  The timeoutInterval value is described to  
begin at x and is doubled until the specified timeoutInterval  
value is reached on the last retry.  This is not how the  
timeoutInterval value actually works.  The first status poll  
to a device uses the timeoutInterval value specified.  If the  
device replies within this time, then the value is decremented  
by 1 second.  The value will continue to be decremented until  
it reaches either 1 second or the device no longer responds to  
the poll within the time.  When the device no longer responds  
within the time, then the timeoutInterval value is increased  
by 1 second, except on the last retry the timeoutInterval value  
is increased to the full value specified plus 1 second.

The ovsnmp.conf man page has been updated to correct the description  
of the timeoutInterval value.      


Leslie A. Clark
IBM Global Services - Systems Mgmt & Networking
(248) 552-4968 Voicemail, Fax, Pager

"Evans, Bill" <Bill.Evans@hq.doe.gov>
Sent by: owner-nv-l@lists.us.ibm.com

06/24/2005 04:49 PM
Please respond to

"'nv-l@lists.us.ibm.com'" <nv-l@lists.us.ibm.com>
RE: [nv-l] Status Polling

Your description was much clearer than mine.  

        "NetView compensates by its geometrically increasing waits on retries"  

Translation: "Every retry doubles the timeout value" = "a geometric progression".  

The NetView for Administrators class also used to warn attendees not to set the retries and wait time so high that the total exceeded the polling cycle.  Your example of 7 retries with 1 second timeout would exceed a two minute polling cycle.   NetView Administration is not for the arithmetically challenged or those who don't appreciate the relationships among the tuning values.  

Thanks for clearing up my muddy wording.

Bill Evans

-----Original Message-----
From: owner-nv-l@lists.us.ibm.com [
mailto:owner-nv-l@lists.us.ibm.com] On Behalf Of Barr, Scott
Sent: Friday, June 24, 2005 4:28 PM

To: nv-l@lists.us.ibm.com

Subject: RE: [nv-l] Status Polling

One warning about retries.

Each time you retry, the SNMP or ping, netmon appears to double the
timeout value. So, if you set 7 retries with 1 second time out, you get

1, 2, 4, 8, 16, 32, 64 seconds timeout values.

If you have a lot of nodes this way, that can cause more issues than it

One caveat, I've been doing TEC/Framework/ITM for a while so the way
netmon behaves may have changed some time ago.

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