Utilities for map/reducing Luwak data

Description

The main purpose of this application is to expose a function that conforms to Riak’s dynamic map/reduce inputs interface, allowing a user to compute a map/reduce query over a Luwak file (see src/luwak_mr.erl). An example use is also included for reference (src/luwak_mr_words.erl).

Setup

To use it, build the project. First edit rebar.config such that the include path in the erl_opts line points to the “luwak-*/include” directory in your Riak installation (the home of luwak.hrl). Then run:

rebar compile

Add the path to the beams to each of your Riak nodes by either adding an ‘add_paths’ setting to the riak_kv section of your app.config before starting the nodes, or by using code:add_path from each node’s console.

Use

You can map/reduce across any Luwak file using the Erlang client:

C:mapred({modfun, luwak_mr, file, <<"my_file_name">>},
         [... your query ...]).

Or HTTP:

{"inputs":{"module":"luwak_mr",
           "function":"file",
           "arg":"my_file_name"},
 "query":[... your query ...]}

If you start your query with a map phase, your map function will be evaluated for each luwak_block object in the file. The KeyData argument to the function will be the block’s offset in the file.