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jan pushed a commit to branch improve-reduce-limit-errors
in repository https://gitbox.apache.org/repos/asf/couchdb.git

commit b030a8648214d88411191dd74f65ee4edc0ed7a2
Author: Paul J. Davis <[email protected]>
AuthorDate: Thu Sep 7 14:37:36 2017 -0500

    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.
---
 src/couch/src/couch_query_servers.erl      | 29 ++++++++++++++++++++++++-----
 src/couch_mrview/src/couch_mrview_http.erl |  6 +++++-
 src/fabric/src/fabric_util.erl             |  2 --
 src/fabric/src/fabric_view.erl             |  2 ++
 test/javascript/tests/view_errors.js       |  4 ++--
 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 63b0e39..4928eea 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 9ad50ee..004caef 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 bf3f023..49f4c89 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 45262e4..dd0fcfd 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 b53a3c7..0d9cd79 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});

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