Large subnet patch

[David W. Hankins]

On Wed, Mar 30, 2005 at 04:53:49PM -0700, Michael Loftis wrote:
> ...or going to some sort of on-disk database instead of 
> in-memory...possibly/probably with a cache or pool in memory.  i 

for v4 that approach would work, and we already have many of the tools
necessary to do so (omapi references and lookup functions find leases).
in any case this is a commonly requested feature (for which user-patches
already exist) that needs to be reviewed and incorporated in one form or
another.  the 'replayable log' format seems most efficient to me, but many
folks seem to have a serious religion for "real databases," possibly for
good reason.

but for v6, we'll still need to be able to forget, in terms of on-disk
storage, the majority of leases (minus the active ones).  2^64 (or more)
lease records is on that order of magnitude that is uncomfortably large
even when on disk.


so i think the right answer is both.

> know.....you shouldn't be serving that many hosts with a single DHCP 
> server, but, i'm just saying.  i'm not saying you must do this or anything. 

several people have complained to me that:

	subnet 10.0.0.0 netmask 255.0.0.0 {
		range 10.0.0.10 10.255.255.254;
	}

with a null dhcpd.leases file results in an uncomfortably long load time,
during which the daemon rapidly uses more and more memory...

these are mostly appliance vendors.

these people don't actually expect to use 2^24 leases actively, it's
some intent not to give their product a listed limit in the number of
leases available.

some would prefer to use a competing dhcp software product which is O(n^2)
in allocating a lease to every client (a linear search on every request).

evidently, putting a specification label on your product that indicates
a limit in the number of leases available is not preferrential to having
that product perform poorly as more leases are allocated.


i'm not defending this standpoint, i think it's ludicrous, i'm just
pointing out that people might not actually expect to use large number of
leases, but will still believe they have reason to configure for them.

and not just for the reason that in ipv6 everyone has a large number of
leases.

> just sticking my $0.02 in (possibly where it doesn't belong ;))

no, this is precisely where it belongs.

-- 
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