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16 changes: 15 additions & 1 deletion draft/use-cases/social-networking-updates-and-profiles.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -112,6 +112,10 @@ Consider the following features of this schema:
sub-document, so that you may iterate the schema can evolve as
necessary without affecting other fields.

.. storing followers in a list would not work well at all in case like twitter, it would grow way too large.
should only store people that user is following, and index that to get follower list of a user.
Also could use a mapping table for further flexibility in relationship.

Posts, of various types, reside in the ``social.post`` collection:

.. code-block:: javascript
Expand Down Expand Up @@ -250,6 +254,11 @@ Consider the following features of this schema:
certain number of comments because the :operator:`$size` query
operator does not allow inequality comparisons.

.. not sure this collection is useful, instead just use the post collection.
Posts should have an index on {user, time} and hence it is efficient to retrieve the wall.
Also wall may be scrolled down to get further items.
Dont think it's worth updating this document every time a user posts.

The second dependent collection is is ``social.news``, which collects
posts from people the user follows. These documents duplicate
information from the documents in the ``social.wall`` collection:
Expand All @@ -263,11 +272,16 @@ information from the documents in the ``social.wall`` collection:
posts: [ ... ]
}

.. This is probably too expensive.
If someone is followed by 1000+ people, that's a lot of documents to write to.
Instead system should use a $in query with people that user is following, sorted by time, with a limit.
This query is actually slow today but got improved a lot in 2.2 and there are good workarounds with 2.0.

Operations
----------

The data model presented above optimizes for read performance at the
possible expense of write performance. To As a result, you should ideally
possible expense of write performance. As a result, you should ideally
provide a queueing system for processing updates which may take longer
than your desired web request latency.

Expand Down