RE: [nv-l] Status Polling myth

[Oliver Bruchhaeuser <oliver.bruchhaeuser@de.ibm.com>]

Demystification #2:

the "Retry Count" value in
the SNMP Configuration dialog actually means the total number of pings
or snmp requests. Including the initial one.
It is planned to change the confusing
wording in this dialog in the future.

Oliver

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

27.06.2005 19:40

Please respond to
nv-l

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

Thank you for setting me straight.
  I never could find an official explanation for the older behavior
and that increment/decrement  comment didn't make sense.  Since
there never was an easy means of directly observing what that behavior
was I've been working with an outdated presentation based on poorly documented
initial information from WAY back on NetView Version 4.  At least
I wasn't alone in my error of understanding.  

I hope someday they'll get the Administrator's Reference and the Man Pages
updated to how it behaves today.  The note that the value will "remain
as configured" isn't very informative and I'm afraid I misread it
as "working as it previously did".  It would help if they
simply stated (and I hope this is correct):

     "NetView will wait <timeoutvalue> tenths of seconds
for an SNMP or ICMP
      reply and if one does not arrive it will retry the
query up to <retryvalue>
      additional times. An error is returned if a response
is not received on any of
      the attempts."  

I'm never sure on these configurations whether the value configured is
the total number of attempts or the number of retries.  At least one
of the IBM Tivoli products is confusing in that regard.  The XNMSNMPCONF
menu is also confusing since it displays the data and has you enter the
timeout value in seconds.  It then records the value in OVSNMP.CONF
(and the database) in tenths of seconds and  XNMSNMPCONF –RES also
displays in tenths of a second.  

My apologies to those I misled (including me).  I will now feel safe
in my own system in setting longer timeout values than I have been using
and it may fix some problems we occasionally have with nodes which are
two WAN hops away from home.   

Bill
 
-----Original Message-----
From: owner-nv-l@lists.us.ibm.com [mailto:owner-nv-l@lists.us.ibm.com]
On Behalf Of Leslie Clark
Sent: Monday, June 27, 2005 12:17 PM
To: nv-l@lists.us.ibm.com
Subject: RE: [nv-l] Status Polling myth
 

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 
TIMEOUT VALUE FOR STATUS POLL IS INCREASED BY 1 SECOND, BUT
MAN PAGE STATES AN EXPONENTIAL ALGORITHM IS USED.

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.       



Cordially,

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

To	"'nv-l@lists.us.ibm.com'" <nv-l@lists.us.ibm.com>
cc
Subject	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
solves.

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