Optimizing performance problems with Aeson rendering large Text arrays

Hello,

In summary, i'm working on an application that responds to a users query, a
sequence index, with the union of a list of UUIDs that have "changed" 
since that
same sequence index, split into 6 sections. I wish to respond to these 
queries
via JSON to provide an easy to use web service, and for the most part, 
what I
have works.

The problem I am having is that profiling seems to show that the 
majority of the
time spent in my application is encoding this to JSON, and also that the
application is only 60% productive with 40% allocations happening in
Data.Aeson.encode (and friends).

Here's an overview of what I'm doing, the full code can be found at the 
end of
this email.

I am storing my data in memory as an IntMap, from sequence index to a 
changeset:

     IntMap ChangeSet

Where a ChangeSet is essentially a tuple of HashSet's of UUIDs:

     data ChangeSet = ChangeSet { artistChanges :: !(HashSet MBID)
                                , labelChanges :: !(HashSet MBID)