Large leases file and long startup time

[David W. Hankins]

On Wed, Jun 30, 2010 at 09:08:47AM -0400, Jason Antman wrote:
> We're running DHCPd (currently 3.0.5) to serve a bunch of networks that
> are mostly static, some dynamic. At the moment, it's 431 subnets, 1762
> clients. We're currently using 3.0.5 with Masney's LDAP patch, but have
> been having some serious startup time issues - on the order of 5
> minutes. I did some investigation with static configs (compiled exactly
> from what's in LDAP) and the time is more or less the same. It appears
> that the bottleneck is reading the leases file, which is on the order of
> 2.3M on our production boxes (with only about 10% max of our clients
> active).

Some "hacks" to improve initial database read performance were pulled
up (we received a patch from the community) either in 3.1.0 or 4.0.0,
I can't remember offhand.  3.1.0 also saw several minor changes to
internal memory structures (hash table sizes and hash algorithm
changes) that significantly enhanced performance at startup and also
runtime.

In general, I would not run 3.0.5.

> Has anyone else found similar issues? Is there any conceivable solution
> - reading the leases file from a database, or storing it in something
> more optimized than a text file?

Not for the leases file yet, no.

The actual problem in my understanding is with the in-memory database,
so just changing the on-disk database would probably not be a complete
solution.  The "log" nature of the text database does make the
problems with the current in-memory database particularly hard to bear
(one 'update' is costly, this cost is multiplied by the number of
times a given lease is recorded in the log), but performance gain
results would probably vary wildly.

-- 
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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