This changes `from django.utils.importlib import import_module` to
`from importlib import import_module`, as `django.utils.importlib` will
be removed in django version 1.9.
I move these three functions to lib/cache.py:
to_dict_cache_key_id
to_dict_cache_key
flush_message
This will prepare us for a more significant refactoring that
eventually breaks down some circular dependencies with
Message and bugdown.
The message cache filling script actually used both database and
memcached queries as part of filling the cache (all used to compute
the needed display_recipient values). We would ideally fix this by
using bulk operations to fill the display_recipient cache, but until
we do so, this cache filler is counterproductive.
I believe this disabling fixes an issue where memcached would get
overloaded and stop handling requests during a server restart on busy
servers.
Originally this cache was used to transmit data from Django to Tornado
(and also for general message caching purposes), but now nothing
actually reads from this cache, so we can eliminate it.
Apparently, the message cache we were filling was completely useless
and unused, and furthermore, the cache we were filling as part of
restarting the server was also totally useless, since it didn't have
the messages users would be requesting.
This changes the type annotations for the cache keys in Zulip to be
consistently text_type, and updates the annotations for values that
are used as cache keys across the codebase.
This needs to be deployed to both staging and prod at the same
off-peak time (and the schema migration run).
At the time it is deployed, we need to make a few changes directly in
the database:
(1) UPDATE django_content_type set app_label='zerver' where app_label='zephyr';
(2) UPDATE south_migrationhistory set app_name='zerver' where app_name='zephyr';
(imported from commit eb3fd719571740189514ef0b884738cb30df1320)
