Re: [RFC] Crazy idea for deferring hosts in progress to a later hostgroup

[Fyodor <fyodor () nmap org>]

On Thu, Mar 26, 2015 at 8:30 AM, Daniel Miller <bonsaiviking () gmail com>
wrote:

> List,
>
> This is a crazy idea, but I think it might work. First, the problem: Nmap
> (portscan phase) scans hosts in a large group (hostgroup), and while some
> hosts may finish quickly, a few slow systems may drag on for a long time,
> preventing new hosts from being scanned until they are finished.
>
> I propose that these slow hosts be identified and "frozen," then added to
> the next hostgroup to be scanned. This way, new (potentially fast) hosts
> can be scanned while these slow ones are finishing.

Hi Dan.  Thanks for sending such an interesting idea.  Right now (as you
know) hosts are scanned in groups, where we do host discovery on all of
them, and after they are all finished we stick them all into port scanning
and then version detection and so forth.  This is definitely non-optimal.
And I hope we're able to eventually move to more of a pipeline system
where, when a single host finishes one phase, it can immediately move to
the next one and you don't end up with a whole group waiting on a few
laggards.

But the approach you mentioned potentially be a good stopgap between the
current situation and the ideal one.  It is always nice to speed things
up.  My only big concern is whether it is worth devoting engineering and
testing/debugging resources to a stopgap or if it's better to wait until we
can tackle the whole problem.  Also, this optimization would mean
reordering the hosts in output.  I don't think that would be a big issue
for most people though.  But some would probably be annoyed by hosts
arriving mostly in order except certain slow hosts appear much later in the
results by the time Nmap may be scanning a completely different subnet.

Cheers,
Fyodor

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