Return reduce overflow errors to the client

This changes the reduce overflow error to return an error to the client
rather than blowing up the view build. This allows views that have a
single bad reduce to build while not crushing the server's RAM usage.

5 files changed, 33 insertions, 10 deletions

diff --git a/src/couch/src/couch_query_servers.erl b/src/couch/src/couch_query_servers.erl
index 63b0e3900..4928eea32 100644
--- a/src/couch/src/couch_query_servers.erl
+++ b/src/couch/src/couch_query_servers.erl
@@ -125,20 +125,39 @@ os_reduce(Lang, OsRedSrcs, KVs) ->
     Proc = get_os_process(Lang),
     OsResults = try proc_prompt(Proc, [<<"reduce">>, OsRedSrcs, KVs]) of
         [true, Reductions] -> Reductions
+    catch
+        throw:{reduce_overflow_error, Msg} ->
+            [{[{reduce_overflow_error, Msg}]} || _ <- OsRedSrcs]
     after
         ok = ret_os_process(Proc)
     end,
     {ok, OsResults}.
 
 os_rereduce(Lang, OsRedSrcs, KVs) ->
-    Proc = get_os_process(Lang),
-    try proc_prompt(Proc, [<<"rereduce">>, OsRedSrcs, KVs]) of
-        [true, [Reduction]] -> Reduction
-    after
-        ok = ret_os_process(Proc)
+    case get_overflow_error(KVs) of
+        undefined ->
+            Proc = get_os_process(Lang),
+            try proc_prompt(Proc, [<<"rereduce">>, OsRedSrcs, KVs]) of
+                [true, [Reduction]] -> Reduction
+            catch
+                throw:{reduce_overflow_error, Msg} ->
+                    {[{reduce_overflow_error, Msg}]}
+            after
+                ok = ret_os_process(Proc)
+            end;
+        Error ->
+            Error
     end.
 
 
+get_overflow_error([]) ->
+    undefined;
+get_overflow_error([{[{reduce_overflow_error, _}]} = Error | _]) ->
+    Error;
+get_overflow_error([_ | Rest]) ->
+    get_overflow_error(Rest).
+
+
 builtin_reduce(_Re, [], _KVs, Acc) ->
     {ok, lists:reverse(Acc)};
 builtin_reduce(Re, [<<"_sum",_/binary>>|BuiltinReds], KVs, Acc) ->
diff --git a/src/couch_mrview/src/couch_mrview_http.erl b/src/couch_mrview/src/couch_mrview_http.erl
index 9ad50eeef..004caef09 100644
--- a/src/couch_mrview/src/couch_mrview_http.erl
+++ b/src/couch_mrview/src/couch_mrview_http.erl
@@ -440,7 +440,11 @@ row_to_json(error, Row) ->
     % match prior behavior.
     Key = couch_util:get_value(key, Row),
     Val = couch_util:get_value(value, Row),
-    Obj = {[{key, Key}, {error, Val}]},
+    Reason = couch_util:get_value(reason, Row),
+    ReasonProp = if Reason == undefined -> []; true ->
+        [{reason, Reason}]
+    end,
+    Obj = {[{key, Key}, {error, Val}] ++ ReasonProp},
     ?JSON_ENCODE(Obj);
 row_to_json(Id0, Row) ->
     Id = case Id0 of
diff --git a/src/fabric/src/fabric_util.erl b/src/fabric/src/fabric_util.erl
index bf3f023db..49f4c8913 100644
--- a/src/fabric/src/fabric_util.erl
+++ b/src/fabric/src/fabric_util.erl
@@ -203,8 +203,6 @@ get_shard([#shard{node = Node, name = Name} | Rest], Opts, Timeout, Factor) ->
         rexi_monitor:stop(Mon)
     end.
 
-error_info({{<<"reduce_overflow_error">>, _} = Error, _Stack}) ->
-    Error;
 error_info({{timeout, _} = Error, _Stack}) ->
     Error;
 error_info({{Error, Reason}, Stack}) ->
diff --git a/src/fabric/src/fabric_view.erl b/src/fabric/src/fabric_view.erl
index 45262e4eb..dd0fcfd8b 100644
--- a/src/fabric/src/fabric_view.erl
+++ b/src/fabric/src/fabric_view.erl
@@ -258,6 +258,8 @@ find_next_key([], _, _, _) ->
 find_next_key([Key|Rest], _, _, _) ->
     {Key, Rest}.
 
+transform_row(#view_row{value={[{reduce_overflow_error, Msg}]}}) ->
+    {row, [{key,null}, {id,error}, {value,reduce_overflow_error}, {reason,Msg}]};
 transform_row(#view_row{key=Key, id=reduced, value=Value}) ->
     {row, [{key,Key}, {value,Value}]};
 transform_row(#view_row{key=Key, id=undefined}) ->
diff --git a/test/javascript/tests/view_errors.js b/test/javascript/tests/view_errors.js
index b53a3c764..0d9cd79fb 100644
--- a/test/javascript/tests/view_errors.js
+++ b/test/javascript/tests/view_errors.js
@@ -174,9 +174,9 @@ couchTests.view_errors = function(debug) {
       // if the reduce grows to fast, throw an overflow error
       var path = "/" + db_name + "/_design/testbig/_view/reduce_too_big";
       xhr = CouchDB.request("GET", path);
-      T(xhr.status == 500);
+      T(xhr.status == 200);
       result = JSON.parse(xhr.responseText);
-      T(result.error == "reduce_overflow_error");
+      T(result.rows[0].error == "reduce_overflow_error");
 
       try {
           db.query(function() {emit(null, null)}, null, {startkey: 2, endkey:1});