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RE: PSINet/Cogent Latency

  • From: Phil Rosenthal
  • Date: Tue Jul 23 02:27:59 2002

I have a small RRD project box that polls 200 interfaces and has it
takes 1 minute, 5 seconds to run with 60%  cpu usage (so obviously it
can be streamlined if I wanted to work on it). I guess the limit in this
implementation is 1000 interfaces per box in this setup -- but I see
most of the CPU usage is in the forking of snmpget over and over.  Im
sure I could write a small program in C that could do this at least 10X
more efficiently.  That's 10,000 interfaces with RRD on one intel -- if
you are determined to do it.

I think if you are billing 10k interfaces, you can afford a 2nd intel
box to check the 2nd 10,000, no?

My point is that if you have sufficient clue, time, and motivation --
Today's generic PCs are capable to do many "large" tasks... 

--Phil


-----Original Message-----
From: Richard A Steenbergen [mailto:ras@e-gerbil.net] 
Sent: Tuesday, July 23, 2002 2:10 AM
To: Phil Rosenthal
Cc: 'Doug Clements'; nanog@merit.edu
Subject: Re: PSINet/Cogent Latency


On Tue, Jul 23, 2002 at 01:56:45AM -0400, Phil Rosenthal wrote:
> 
> I don't think RRD is that bad if you are gonna check only every 5 
> minutes...

RRD doesn't measure anything, it stores and graphs data. The perl
pollers everyone is using can barely keep up with 5 minute samples on a
couple dozen routers and a few hundred interfaces, requiring "poller
farms" to be distributed across a network, 'lest a box or part of the
network break and you lose data.

> Again, perhaps I'm just missing something, but so lets say you measure

> 30 seconds late , and it thinks its on time -- So that one sample will

> be higher , then the next one will be on time, so 30 seconds early for

> that sample -- it will be lower.  On the whole -- it will be accurate 
> enough -- no?

"enough" is a relative term, but sure. :)

> I'm not saying a hardware solution can't be better -- but it is likely

> overkill compared to a few cheap intels running RRD -- assuming your 
> snmpd can deal with the load...

What hardware... storing a few byte counters is trivial, but polling
them through snmp is what is hard (never trust a protocol named "simple"
or "trivial"). Creating a buffer of samples which can be periodically
sampled should be easy and painless. I don't know if I call periodic ftp

"painless" but its certainly a start.

-- 
Richard A Steenbergen <ras@e-gerbil.net>
http://www.e-gerbil.net/ras
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