Testing tanodb preflist generation

tanodb-preflist.markdown

tanodb is a distributed in memory key value store built on top of riak_core.

It is used as the example code for the Little Riak Core Book.

(kudos to @cv for the original version)

I found the following piece of code in a gist, but when I tried to execute it under taminodb, it returned an empty array.

(tanodb3@127.0.0.1)7> Preflist = fun(Bucket,Key) ->
(tanodb3@127.0.0.1)7>   BKey = {Bucket,Key},
(tanodb3@127.0.0.1)7>   {ok, Ring} = riak_core_ring_manager:get_my_ring(),
(tanodb3@127.0.0.1)7>   DocIdx = riak_core_util:chash_key(BKey),
(tanodb3@127.0.0.1)7>   BucketProps = riak_core_bucket:get_bucket(Bucket, Ring),
(tanodb3@127.0.0.1)7>   [NValue] = [Y || {X1, Y} <- BucketProps, n_val == X1],
(tanodb3@127.0.0.1)7>   UpNodes = riak_core_node_watcher:nodes(riak_kv),
(tanodb3@127.0.0.1)7>   Preflist2 = riak_core_apl:get_apl_ann(DocIdx, NValue, Ring, UpNodes),
(tanodb3@127.0.0.1)7>   [IndexNode || {IndexNode, _Type} <- Preflist2]
(tanodb3@127.0.0.1)7> end.
#Fun<erl_eval.12.54118792>
(tanodb3@127.0.0.1)8> Preflist(<<"foo">>,<<"bar">>).
[]

Let's take a look at the implementation, and the debugging and steps required for it to execute correctly on a running Tanodb instance.

(tanodb3@127.0.0.1)16> f().
ok
(tanodb3@127.0.0.1)17>  Bucket = <<"foo">>.
<<"foo">>
(tanodb3@127.0.0.1)18>   Key = <<"bar">>.
<<"bar">>
(tanodb3@127.0.0.1)19>   BKey = {Bucket,Key}.
{<<"foo">>,<<"bar">>}
(tanodb3@127.0.0.1)20>   {ok, Ring} = riak_core_ring_manager:get_my_ring().
{ok,{chstate_v2,'tanodb3@127.0.0.1',
        [{'tanodb3@127.0.0.1',{18,63615060109}},
         {'tanodb1@127.0.0.1',{110,63615060109}},
         {'tanodb2@127.0.0.1',{10,63615060107}}],
        {64,
         [{0,'tanodb1@127.0.0.1'},
          {22835963083295358096932575511191922182123945984,
           'tanodb2@127.0.0.1'},
          {45671926166590716193865151022383844364247891968,
           'tanodb2@127.0.0.1'},
          {68507889249886074290797726533575766546371837952,
           'tanodb3@127.0.0.1'},
          {91343852333181432387730302044767688728495783936,
           'tanodb1@127.0.0.1'},
          {114179815416476790484662877555959610910619729920,
           'tanodb2@127.0.0.1'},
          {137015778499772148581595453067151533092743675904,
           'tanodb2@127.0.0.1'},
          {159851741583067506678528028578343455274867621888,
          [.......]

(tanodb3@127.0.0.1)21>   DocIdx = riak_core_util:chash_key(BKey).
<<73,212,27,234,104,13,150,207,0,82,86,183,125,225,172,
  154,135,46,6,112>>

(tanodb3@127.0.0.1)22> BucketProps = riak_core_bucket:get_bucket(Bucket, Ring).
[{name,<<"foo">>},
 {allow_mult,true},
 {basic_quorum,false},
 {big_vclock,50},
 {chash_keyfun,{riak_core_util,chash_std_keyfun}},
 {dvv_enabled,true},
 {dw,quorum},
 {last_write_wins,false},
 {linkfun,{modfun,riak_kv_wm_link_walker,mapreduce_linkfun}},
 {n_val,3},
 {notfound_ok,true},
 {old_vclock,86400},
 {postcommit,[]},
 {pr,0},
 {precommit,[]},
 {pw,0},
 {r,quorum},
 {rw,quorum},
 {small_vclock,50},
 {w,quorum},
 {young_vclock,20}]
(tanodb3@127.0.0.1)23>

(tanodb3@127.0.0.1)23>  [NValue] = [Y || {X1, Y} <- BucketProps, n_val == X1].
[3]
(tanodb3@127.0.0.1)24>  UpNodes = riak_core_node_watcher:nodes(riak_kv).
[]

So it looks like we aren't running any nodes which are using Riak KV. In retrospect that's pretty obvious, we are running Taminodb, after all.

(tanodb3@127.0.0.1)25> riak_core_node_watcher:services().
[tanodb]
(tanodb3@127.0.0.1)28> f(UpNodes).
ok

Lets try again to generate the preflist, this time when trying to retrieve the running nodes, lets use tanodb as the service name.

(tanodb3@127.0.0.1)29>  UpNodes = riak_core_node_watcher:nodes(tanodb).
['tanodb1@127.0.0.1','tanodb2@127.0.0.1',
 'tanodb3@127.0.0.1']

Success! Lets generate the preflist!

(tanodb3@127.0.0.1)31>  Preflist2 = riak_core_apl:get_apl_ann(DocIdx, NValue, Ring, UpNodes).
[{{433883298582611803841718934712646521460354973696,
   'tanodb3@127.0.0.1'},
  primary},
 {{456719261665907161938651510223838443642478919680,
   'tanodb1@127.0.0.1'},
  primary},
 {{479555224749202520035584085735030365824602865664,
   'tanodb2@127.0.0.1'},
  primary}]

So, finally, the finished version:

% Example : Preflist({<<"bucket">>,<<"key">>}}.
%
Preflist = fun(Bucket,Key) ->
  BKey = {Bucket,Key},
  {ok, Ring} = riak_core_ring_manager:get_my_ring(),
  DocIdx = riak_core_util:chash_key(BKey),
  BucketProps = riak_core_bucket:get_bucket(Bucket, Ring), 
  [NValue] = [Y || {X1, Y} <- BucketProps, n_val == X1],
  UpNodes = riak_core_node_watcher:nodes(tanodb),
  Preflist2 = riak_core_apl:get_apl_ann(DocIdx, NValue, Ring, UpNodes),
  [IndexNode || {IndexNode, _Type} <- Preflist2]
end.