New (?) idea to optimize database

[.rp]

From:           	David Relson <relson at osagesoftware.com>
Copies to:      	bogofilter at bogofilter.org
Date sent:      	Sat, 18 Mar 2006 14:20:46 -0500
Subject:        	Re: New (?) idea to optimize database

> On Sat, 18 Mar 2006 16:04:54 +0100
> Boris 'pi' Piwinger wrote:
> 
> > Hi!
> > 
> > We had lengthy discussions how to optimize (=minimize) the
> > database to get best performance. This is why I created
> > bogominitrain. Now clearly, this will also collect useless
> > tokens. Now here is the idea to improve:
> > 
> > Do bogominitrain, remove all tokens which show up only once
> > in the training body (to do so, full training is needed in
> > a separate body). Also prevent those tokens from being added
> > again and do bogominitrain again. Repeat until is converged.
> 
> Hi pi,
> 
> Interesting idea!
> 
> Clearly the "prevent" part is a problem as it implies a "prevent"
> database and bogofilter lacks such a concept hence couldn't use
> prevent.db even if it existed.
> 
>[...] 

I don't understand what is meant by converge 
and
couldn't the "ignore" be used as a "prevent" for purposes of train?