[Opendnssec-develop] Signer Testplan: first try

Rick van Rein rick at openfortress.nl
Wed Apr 8 20:09:40 UTC 2009


You woke up the tiny mathematician living inside my head!

> In my world, jitter is ABS(MAX(VARIANCE(signature expiration time))).

1. You must mean MAX(ABS(...)) and not ABS(MAX(...))

2. I don't think you intended to use VARIANCE as a consolidation function,
   which is how statistics defines it; I think your intention is to calculate
   a difference with a mean value and have the consolidation done by MAX?

3. Instead of VARIANCE (which is a square of the (standard) deviation from
   the mean value) you probably mean the deviation.

I think I would capture your intentions in formulae as follows:

M = Average_i (sigexptime_i)
Jitter = Max_i (Abs (sigexptime_i - M))

Average_i and Max_i are consolidation functions ranging over i,
and sigexptime_i is the time of the i'th signature expiration.

>   signature expiration = calculated expiration time - jitter +  
> (random(jitter) * 2)
> where random(x) is a function generating a random numberr such as 0 ≤  
> r ≤ x. this would generate a signature exception that can vary +/-  
> some jitter number of seconds, right?


> >- Is random jitter acceptable?
> not only acceptable, it is required.

I missed the background of jitter, perhaps we can clear it up?

Is Jitter a feature (a way of spreading signatures over time if a lot
of work would otherwise come in at once) or a bug (the result of the
non-ideal OS and such)?

I cannot help but feel that we are re-inventing realtime scheduling here.

Hope this helps,


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