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From Paul Hirst <paul.hi...@sophos.com>
Subject Erlang views and static data
Date Thu, 12 Jul 2012 08:12:11 GMT
Hi,

I'm currently rewriting some of my views in Erlang because I've had trouble with a few large
documents exploding up the javascript interepreter and that's a good excuse to switch to Erlang
and gain some extra performance too.

I have one view which is rather complex and which contains 2 dictionaries (hashes, objects,
whatever you want to call them) each of around 150 elements. These are used to remap some
of the data from one form to another. Every 6 months or so I need to add a couple of new entries
to these and in the past that has meant rebuilding the whole view which takes a few days.
That's all ok but I'm wondering how best to deal with this now I'm reimplementing in Erlang.

Firsly I'm not sure of the efficiencies of doing something like this:

Fun({Doc}) ->
  Lookup1 = [{<<"foo">>,<<"bar">},{<<"baz">>,<<"wibble">>},....],
  %% Rest of the code which actually uses Lookup1
  OldVal = proplist:get_value(<<"to_remap">>, Doc),
  NewVal = proplist:get_value(OldVal, Lookup1),
  Emit(NewVal, something...)
end.

Will Lookup1 get recreated every time a document is processed by the view, or every time the
view updater is kicked, or something else?

My example shows a proplist. It sounds like I should actually use a dict structure. It looks
like I can pass in the same list but run it through dict:from_list/1. That's all fine but
my questions about efficiency apply even more.

Should/Can I keep this data outside of the view code? I fully understand the need to detect
changes which alter the view output but in this case I can actually cheat by promising to
only ever add entries, and to always add entries to the dictionary prior to adding and documents
which require the change. Obviously I would need to tread very carefully but I could read
the data from a file somewhere on disk... or maybe even from another document in the database.

Thanks,
Paul

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