Google App Engine - Tracking which indexes are used
The App Engine SDK tracks this for its automatic index creation. Delete your index.yaml, then give your app a good workout. As long as you hit every distinct query in your testing, the SDK will generate a new index.yaml that contains only the indexes you need.
I have a App Engine/Python/Django application which has grown and been modified over the past year and currently has 175 indexes. The problem is that I have not been thourough in cleaning up/removing indexes that are no longer needed. Now,  I am not sure which indexes are active and which are essentially dead, but I am guessing that about 20% of the idexes are useless.
I am curious if there are any App Engine tools available for tracking/counting number of accesses to indexes? 
If no tools are available, then one possible idea is to overload the fetch method to track this information everytime an index is accessed, but I am not sure if this is a good idea (could slow things down) and I don't know what the best way to implement this might be. 
If anybody has already gone through the experience of cleaning up (searching for) dead indexes, I would be interested in hearing about your experiences.