Add _approx_count_distinct as a builtin reduce function

LICENSE

@@ -2274,3 +2274,27 @@ HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 SUCH DAMAGE.
+
+For the src/hyper component:
+
+The MIT License (MIT)
+
+Copyright (c) 2014 Game Analytics ApS
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

NOTICE

@@ -184,3 +184,7 @@ This product also includes the following third-party components:
  1997 Niels Provos <[email protected]>
  - The asynchronous queue code (c_src/async_queue.c and c_src/async_queue.h)
  is from the esnappy project, copyright 2011 Konstantin V. Sorokin.
+
+* hyper
+
+ Copyright (c) 2014 Game Analytics ApS

rebar.config.script

@@ -61,6 +61,7 @@ DepDescs = [
  {tag, "v1.1.15"}, [raw]},
 %% Third party deps
 {folsom, "folsom", {tag, "CouchDB-0.8.2"}},
+{hyper, "hyper", {tag, "CouchDB-2.2.0-3"}},
 {ibrowse, "ibrowse", {tag, "CouchDB-4.0.1"}},
 {jiffy, "jiffy", {tag, "CouchDB-0.14.11-2"}},
 {mochiweb, "mochiweb", {tag, "v2.17.0"}},

rel/reltool.config

@@ -47,6 +47,7 @@
  fabric,
  folsom,
  global_changes,
+ hyper,
  ibrowse,
  ioq,
  jiffy,
@@ -101,6 +102,7 @@
  {app, fabric, [{incl_cond, include}]},
  {app, folsom, [{incl_cond, include}]},
  {app, global_changes, [{incl_cond, include}]},
+ {app, hyper, [{incl_cond, include}]},
  {app, ibrowse, [{incl_cond, include}]},
  {app, ioq, [{incl_cond, include}]},
  {app, jiffy, [{incl_cond, include}]},

src/couch/src/couch_query_servers.erl

@@ -17,6 +17,7 @@
 -export([reduce/3, rereduce/3,validate_doc_update/5]).
 -export([filter_docs/5]).
 -export([filter_view/3]).
+-export([finalize/1]).
 -export([rewrite/3]).
 
 -export([with_ddoc_proc/2, proc_prompt/2, ddoc_prompt/3, ddoc_proc_prompt/3, json_doc/1]).
@@ -86,6 +87,16 @@ group_reductions_results(List) ->
  [Heads | group_reductions_results(Tails)]
  end.
 
+finalize(Reductions) ->
+ {ok, lists:map(fun(Reduction) ->
+ case hyper:is_hyper(Reduction) of
+ true ->
+ round(hyper:card(Reduction));
+ false ->
+ Reduction
+ end
+ end, Reductions)}.
+
 rereduce(_Lang, [], _ReducedValues) ->
  {ok, []};
 rereduce(Lang, RedSrcs, ReducedValues) ->
@@ -171,7 +182,10 @@ builtin_reduce(rereduce, [<<"_count",_/binary>>|BuiltinReds], KVs, Acc) ->
  builtin_reduce(rereduce, BuiltinReds, KVs, [Count|Acc]);
 builtin_reduce(Re, [<<"_stats",_/binary>>|BuiltinReds], KVs, Acc) ->
  Stats = builtin_stats(Re, KVs),
- builtin_reduce(Re, BuiltinReds, KVs, [Stats|Acc]).
+ builtin_reduce(Re, BuiltinReds, KVs, [Stats|Acc]);
+builtin_reduce(Re, [<<"_approx_count_distinct",_/binary>>|BuiltinReds], KVs, Acc) ->
+ Distinct = approx_count_distinct(Re, KVs),
+ builtin_reduce(Re, BuiltinReds, KVs, [Distinct|Acc]).
 
 
 builtin_sum_rows([], Acc) ->
@@ -303,6 +317,13 @@ get_number(Key, Props) ->
  throw({invalid_value, iolist_to_binary(Msg)})
  end.
 
+% TODO allow customization of precision in the ddoc.
+approx_count_distinct(reduce, KVs) ->
+ lists:foldl(fun([[Key, _Id], _Value], Filter) ->
+ hyper:insert(term_to_binary(Key), Filter)
+ end, hyper:new(11), KVs);
+approx_count_distinct(rereduce, Reds) ->
+ hyper:union([Filter || [_, Filter] <- Reds]).
 
 % use the function stored in ddoc.validate_doc_update to test an update.
 -spec validate_doc_update(DDoc, EditDoc, DiskDoc, Ctx, SecObj) -> ok when

src/couch_mrview/src/couch_mrview.erl

@@ -184,6 +184,8 @@ validate(DbName, DDoc) ->
  ok;
  ({_RedName, <<"_stats", _/binary>>}) ->
  ok;
+ ({_RedName, <<"_approx_count_distinct", _/binary>>}) ->
+ ok;
  ({_RedName, <<"_", _/binary>> = Bad}) ->
  Msg = ["`", Bad, "` is not a supported reduce function."],
  throw({invalid_design_doc, Msg});

src/fabric/src/fabric_view.erl

@@ -230,8 +230,9 @@ get_next_row(#collector{reducer = RedSrc} = St) when RedSrc =/= undefined ->
  end, Counters0, Records),
  Wrapped = [[V] || #view_row{value=V} <- Records],
  {ok, [Reduced]} = couch_query_servers:rereduce(Lang, [RedSrc], Wrapped),
+ {ok, [Finalized]} = couch_query_servers:finalize([Reduced]),
  NewSt = St#collector{keys=RestKeys, rows=NewRowDict, counters=Counters},
- {#view_row{key=Key, id=reduced, value=Reduced}, NewSt};
+ {#view_row{key=Key, id=reduced, value=Finalized}, NewSt};
  error ->
  get_next_row(St#collector{keys=RestKeys})
  end;

test/javascript/tests/reduce_builtin.js

@@ -37,6 +37,12 @@ couchTests.reduce_builtin = function(debug) {
  emit(doc.integer, doc.integer);
  };
 
+ var check_approx_distinct = function(expected, estimated) {
+ // see https://en.wikipedia.org/wiki/HyperLogLog
+ var err = 1.04 / Math.sqrt(Math.pow(2, 11 - 1));
+ return Math.abs(expected - estimated) < expected * err;
+ };
+
  var result = db.query(map, "_sum");
  T(result.rows[0].value == 2*summate(numDocs));
  result = db.query(map, "_count");
@@ -47,27 +53,41 @@ couchTests.reduce_builtin = function(debug) {
  T(result.rows[0].value.min == 1);
  T(result.rows[0].value.max == 500);
  T(result.rows[0].value.sumsqr == 2*sumsqr(numDocs));
+ result = db.query(map, "_approx_count_distinct");
+ T(check_approx_distinct(numDocs, result.rows[0].value));
 
  result = db.query(map, "_sum", {startkey: 4, endkey: 4});
  T(result.rows[0].value == 8);
  result = db.query(map, "_count", {startkey: 4, endkey: 4});
  T(result.rows[0].value == 2);
+ result = db.query(map, "_approx_count_distinct", {startkey:4, endkey:4});
+ T(check_approx_distinct(1, result.rows[0].value));
 
  result = db.query(map, "_sum", {startkey: 4, endkey: 5});
  T(result.rows[0].value == 18);
  result = db.query(map, "_count", {startkey: 4, endkey: 5});
  T(result.rows[0].value == 4);
+ result = db.query(map, "_approx_count_distinct", {startkey:4, endkey:5});
+ T(check_approx_distinct(2, result.rows[0].value));
+
 
  result = db.query(map, "_sum", {startkey: 4, endkey: 6});
  T(result.rows[0].value == 30);
  result = db.query(map, "_count", {startkey: 4, endkey: 6});
  T(result.rows[0].value == 6);
+ result = db.query(map, "_approx_count_distinct", {startkey: 4, endkey: 6});
+ T(check_approx_distinct(3, result.rows[0].value));
 
  result = db.query(map, "_sum", {group:true, limit:3});
  T(result.rows[0].value == 2);
  T(result.rows[1].value == 4);
  T(result.rows[2].value == 6);
 
+ result = db.query(map, "_approx_count_distinct", {group:true, limit:3});
+ T(check_approx_distinct(1, result.rows[0].value));
+ T(check_approx_distinct(1, result.rows[1].value));
+ T(check_approx_distinct(1, result.rows[2].value));
+
  for(var i=1; i<numDocs/2; i+=30) {
  result = db.query(map, "_sum", {startkey: i, endkey: numDocs - i});
  T(result.rows[0].value == 2*(summate(numDocs-i) - summate(i-1)));