performance with 20000 classes; release a lease manually

David W. Hankins dhankins at
Mon Jun 8 22:58:04 UTC 2009

On Wed, May 27, 2009 at 05:59:58PM +0200, stefan novak wrote:
> My config is very simple and works as expected.
> The client behind the cable modem always gets the fixed address. is
> this config scaleable to 20000 classes, or is there another way to
> configure such a scenario.

The list of classes is searched linearly.  So the complexity in the
trivial system you're describing is something like O(C*H) where C is
the number of classes and H is the number of hosts (disregarding other
presumed-constant factors for the time being).

However, although classes are searched linearly, subclasses attached
to those classes are searched on a hash table, which is hopefully O(1)
for subclass:class ratios less than or equal to 100003:1, but probably
curves somewhere prior to that.  Well after 20,000 I would hope, but
this depends upon our hash algorithm.

So this is a way where I think you can reduce the number of classes
for your cable modems to 1, so the complexity becomes closer to O(H).

There's a section in 'man dhcpd.conf' on subclassing, the default
example is slightly different from what you are looking for, but it
should be easy to see how to use it for this purpose.

David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins
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