Add field to Riak YZ Schema with CRDTs

gistfile1.txt

This gist captures what needs to be done to add a new field to Riak's Yokozuna
search index.

Sources:
- https://github.com/basho/yokozuna/issues/130
- http://riak-users.197444.n3.nabble.com/How-to-update-existed-schema-td4032143.html

The code below is for illustration purposes only. Use at your own risk.

1. Create/Update new schema file
2. Upload schema to main node
   cat schema/my_bucket.xml | curl -XPUT http://127.0.0.1:49001/search/schema/my_bucket -H 'Content-Type:application/xml' --data-binary @-
 
3. Reload YZ index on each node
   a. individual rpc calls on each node:
      rpc:block_call('riak@172.17.0.1', yz_index, reload, [<<"my_bucket">>]).
      rpc:block_call('riak@172.17.0.2', yz_index, reload, [<<"my_bucket">>]).
      rpc:block_call('riak@172.17.0.3', yz_index, reload, [<<"my_bucket">>]).
 
   b. via multicall
      rpc:multicall(['riak@172.17.0.1','riak@172.17.0.2','riak@172.17.0.3'], yz_index, reload, [<<"my_bucket">>]).
 
      If all is well then you should get {ok, Nodes} where Nodes is the
      list of nodes in your Riak cluster. If something goes wrong
      you'll get {error, Errors} where Errors is a list of errors
      for each node that had an error.

  At this point any new data inserted is searchable. To get old data re-indexed
  with new field definition, we need to read/write all keys in the bucket
 
18> {ok, Keys} = riakc_pb_socket:list_keys(Pid, {<<"my_bucket">>,<<"my_bucket">>}).
19> lists:foreach(fun(E) -> {ok, Post} = 
    {ok, M1} = riakc_pb_socket:fetch_type(Pid, {<<"my_bucket">>, <<"my_bucket">>}, E), 
	M2 = riakc_map:update({<<"some_field">>, set}, fun(S) -> riakc_set:add_element(<<"1">>, S), riakc_set:del_element(<<"1">>, S)  end, M1),
    riakc_pb_socket:update_type(Pid, {<<"my_bucket">>, <<"my_bucket">>}, E, riakc_map:to_op(M2)) end, Keys). 

WARNING: the code above can wreck havoc on your cluster, esp. if you have gazillions
of keys. Think carefully. Unfortunately, this is the only way to achieve what we 
need to do as of 06/26/2015