Github user davisp commented on a diff in the pull request:
https://github.com/apache/couchdb-couch/pull/229#discussion_r103793859
--- Diff: src/couch_query_servers.erl ---
@@ -142,25 +142,34 @@ os_rereduce(Lang, OsRedSrcs, KVs) ->
builtin_reduce(_Re, [], _KVs, Acc) ->
{ok, lists:reverse(Acc)};
builtin_reduce(Re, [<<"_sum",_/binary>>|BuiltinReds], KVs, Acc) ->
- Sum = builtin_sum_rows(KVs),
+ Sum = builtin_sum_rows(KVs, []),
builtin_reduce(Re, BuiltinReds, KVs, [Sum|Acc]);
builtin_reduce(reduce, [<<"_count",_/binary>>|BuiltinReds], KVs, Acc) ->
Count = length(KVs),
builtin_reduce(reduce, BuiltinReds, KVs, [Count|Acc]);
builtin_reduce(rereduce, [<<"_count",_/binary>>|BuiltinReds], KVs, Acc) ->
- Count = builtin_sum_rows(KVs),
+ Count = builtin_sum_rows(KVs, []),
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_sum_rows(KVs) ->
- lists:foldl(fun([_Key, Value], Acc) -> sum_values(Value, Acc) end, 0,
KVs).
-sum_values({Props}, 0) ->
- {Props};
-sum_values({Props}, {AccProps}) ->
- {sum_objects(lists:sort(Props), lists:sort(AccProps))};
+builtin_sum_rows([], Acc) ->
+ Acc;
+builtin_sum_rows([[Key, Value] | RestKVs], Acc) ->
+ try sum_values(Value, Acc) of
+ NewAcc ->
+ builtin_sum_rows(RestKVs, NewAcc)
+ catch
+ throw:{builtin_reduce_error, Obj} ->
+ Obj;
+ throw:{invalid_value, Reason, Cause} ->
+ {[{<<"error">>, <<"builtin_reduce_error">>},
--- End diff --
This is because a reduction function has to operate on its own output, not
because of recursion. What we're doing here is setting up a try/catch so that
we can have a non-local return when we detect an error. That error might either
be when doing a reduce and hitting a bad value emitted in the index, or it
might be later on when we're rereducing a group of reductions that contains an
error. In both cases we want to pass the error up immediately and cease
recursion.
Technically we could have split this into two different functions that are
called based on reduce vs rereduce but the existing logic precluded that from
being very simple without a massively more complicated change.
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