This is a multi-steps process:
* get a update's `user_id` from the metadata
* store the `user_id` (`lastUpdatedBy`) and current date (`lastUpdatedAt`) for
the document in Redis on every updates
* fetch `lastUpdatedAt` and `lastUpdatedBy` from Redis on document flush
* send the data to web to be persisted in Mongo
Remove the old pub/sub listener which is no longer used.
Also remove the DocsWithPendingUpdates set, which used to track
docs waiting to be updated. This was necessary incase messages were
missed on the pub/sub channel, so we knew which docs still had pending
updates. However, now we use the BLPOP queue, these updates just sit in
the queue until a consumer comes back to continue consuming them.
In Javascript, characters are 16-bits wide. It does not understand surrogates as characters.
From Wikipedia (http://en.wikipedia.org/wiki/Plane_(Unicode)#Basic_Multilingual_Plane):
"The High Surrogates (U+D800–U+DBFF) and Low Surrogate (U+DC00–U+DFFF) codes are reserved
for encoding non-BMP characters in UTF-16 by using a pair of 16-bit codes: one High Surrogate
and one Low Surrogate. A single surrogate code point will never be assigned a character.""
The main offender seems to be \uD835 as a stand alone character, which would be the first
16-bit character of a blackboard bold character (http://www.fileformat.info/info/unicode/char/1d400/index.htm).
Something must be going on client side that is screwing up the encoding and splitting the
two 16-bit characters so that \uD835 is standalone.
