Every query we use should be able to efficiently use an index, yet
at the same time, we shouldn't create superflous indexes.

Related:


-  `http://kylebanker.com/blog/2010/09/21/the-joy-of-mongodb-indexes/ <http://kylebanker.com/blog/2010/09/21/the-joy-of-mongodb-indexes/>`_
-  `http://www.mongodb.org/display/DOCS/Indexing+Advice+and+FAQ <http://www.mongodb.org/display/DOCS/Indexing+Advice+and+FAQ>`_
-  `http://www.mongodb.org/display/DOCS/Indexes <http://www.mongodb.org/display/DOCS/Indexes>`_

Especially, we should play with using explain:

`http://www.mongodb.org/display/DOCS/Indexing+Advice+and+FAQ#IndexingAdviceandFAQ-Use{{explain <http://www.mongodb.org/display/DOCS/Indexing+Advice+and+FAQ#IndexingAdviceandFAQ-Use%7B%7Bexplain>`_}}.

Assigning to myself, but feel free to claim this if you're excited
about investigating.

When you create an index in indexes.py it's like:

::

    USER_INDEXES = {
        'username_unique': {
            # Index usernames, and make sure they're unique.
            # ... I guess we might need to adjust this once we're federated :)
            'index': 'username',
            'unique': True},
        'created': {
            # All most recently created users
            'index': 'created'}}

However when you remove it, we just keep track on the key/name
there (like 'username\_unique' and drop the rest of the info
because it isn't immediately needed.

::

    DEPRECATED_USER_INDEXES = ['created']

... that's a shame because then we might forget what the original
index was, and all that useful information. Even though that's not
needed, we should keep it around.

I originally wrote the code to be like that, then I changed it.
Time to change it back!

mediagoblin/util.py is like our junk drawer for any functionality
we want to abstract out of a particular view, and it's starting to
get ugly. At present, it contains methods related to: testing,
templating, request processing, user sessions, dynamic component
importing, urls/slugs, email, translation, data sanitizing,and
pagination. Most of these categories are functionally distinct from
the others and could be separated out into different files
according to category, e.g.:

mediagoblin/tools
- tests.py
- templates.py
- requests.py
- text\_processing.py
- etc.

Once a structure is decided upon, imports referencing util.py will
have to be updated.