Acts_as_ferret: Slow ferret_update with associated models

Hi,

I am using some custom fields for ferret indexing to include fields from
associated models. When those child models are updated, I do
ferret_update
on the parent model. Unfortunately, that takes very long, depending on
the
number of associated child models. That is because every child model is
called to re-index the parent, instead of just the changed one.

What can I do to speed up re-indexing?
I am using Rails 2.1.2, Ferret 0.11.6 and ActsAsFerret 0.4.2.
Thanks for your advice!

Best
Jon