> Now you're getting to the technical part. This quote from Damien is
> the best I can do for you:
> http://damienkatz.net/2008/02/incremental_map_1.html
> ... in this design, the reductions happen at index-update time, and
> the reductions are stored directly inside the inner nodes of the view
> b+tree index. Then at query time, the intermediate results are reduced
> to their final result. The number of reductions that happen at query
> time are logarithmic with respect to the number of matching
> key/values.

So for modifications and deletions, the map results are changed, the  
tree of intermediate values is partially dirty, and the reduction only  
has to be partially re-done.

Very cool.