Return reduce overflow errors to the clientimprove-reduce-limit-errors

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});