fix external size bug when seq btree exists (#849)

When users specify "options":  {"seq_indexed": true}, we will run
reduced_external_size/1 on seq btrees. The reduce will return an
integer because the reduce function is:
couch_db_updater:btree_by_seq_reduce/2.
This leads to a bad match error. Thanks @jiangphcn for finding this.

3 files changed, 63 insertions, 12 deletions

diff --git a/src/couch_mrview/src/couch_mrview.erl b/src/couch_mrview/src/couch_mrview.erl
index 07e36687d..83a03ffa1 100644
--- a/src/couch_mrview/src/couch_mrview.erl
+++ b/src/couch_mrview/src/couch_mrview.erl
@@ -314,15 +314,17 @@ count_view_changes_since(Db, DDoc, VName, SinceSeq, Options) ->
                 true -> View#mrview.key_byseq_btree;
                 _ -> View#mrview.seq_btree
             end,
+            RedFun = fun(_SeqStart, PartialReds, 0) ->
+                {ok, couch_btree:final_reduce(Btree, PartialReds)}
+            end,
             lists:foldl(fun(Opts, Acc0) ->
-                            {ok, N} = couch_btree:fold_reduce(
-                                    Btree, fun(_SeqStart, PartialReds, 0) ->
-                                        {ok, couch_btree:final_reduce(
-                                                    Btree, PartialReds)}
-                                    end,
-                                0, Opts),
-                            Acc0 + N
-                    end, 0, OptList);
+                case couch_btree:fold_reduce(Btree, RedFun, 0, Opts) of
+                    {ok, N} when is_integer(N) ->
+                        Acc0 + N;
+                    {ok, N} when is_tuple(N) ->
+                        Acc0 + element(1, N)
+                end
+            end, 0, OptList);
         _ ->
             {error, seqs_not_indexed}
     end.
diff --git a/src/couch_mrview/src/couch_mrview_util.erl b/src/couch_mrview/src/couch_mrview_util.erl
index 0d58e4f35..d26df94f2 100644
--- a/src/couch_mrview/src/couch_mrview_util.erl
+++ b/src/couch_mrview/src/couch_mrview_util.erl
@@ -299,7 +299,7 @@ open_view(Db, Fd, Lang, ViewState, View) ->
     ],
     {ok, Btree} = couch_btree:open(BTState, Fd, ViewBtOpts),
 
-    BySeqReduceFun = fun couch_db_updater:btree_by_seq_reduce/2,
+    BySeqReduceFun = make_seq_reduce_fun(),
     {ok, SeqBtree} = if View#mrview.seq_indexed ->
         SeqBTState = get_seq_btree_state(ViewState),
         ViewSeqBtOpts = [{reduce, BySeqReduceFun},
@@ -804,16 +804,24 @@ reduced_external_size(Tree) ->
     end.
 
 
+reduced_seq_external_size(Tree) ->
+    case couch_btree:full_reduce(Tree) of
+        {ok, {_, Size}} -> Size;
+        % return 0 for older versions that only returned number of docs
+        {ok, NumDocs} when is_integer(NumDocs) -> 0
+    end.
+
+
 calculate_external_size(Views) ->
     SumFun = fun(#mrview{btree=Bt, seq_btree=SBt, key_byseq_btree=KSBt}, Acc) ->
         Size0 = sum_btree_sizes(Acc, reduced_external_size(Bt)),
         Size1 = case SBt of
             nil -> Size0;
-            _ -> sum_btree_sizes(Size0, reduced_external_size(SBt))
+            _ -> sum_btree_sizes(Size0, reduced_seq_external_size(SBt))
         end,
         case KSBt of
             nil -> Size1;
-            _ -> sum_btree_sizes(Size1, reduced_external_size(KSBt))
+            _ -> sum_btree_sizes(Size1, reduced_seq_external_size(KSBt))
         end
     end,
     {ok, lists:foldl(SumFun, 0, Views)}.
@@ -1044,6 +1052,10 @@ get_user_reds(Reduction) ->
     element(2, Reduction).
 
 
+% This is for backwards compatibility for seq btree reduces
+get_external_size_reds(Reduction) when is_integer(Reduction) ->
+    0;
+
 get_external_size_reds(Reduction) when tuple_size(Reduction) == 2 ->
     0;
 
@@ -1072,6 +1084,22 @@ make_reduce_fun(Lang, ReduceFuns) ->
             {Counts, Result, ExternalSize}
     end.
 
+make_seq_reduce_fun() ->
+    fun
+        (reduce, KVs0) ->
+            KVs = detuple_kvs(expand_dups(KVs0, []), []),
+            NumDocs = length(KVs),
+            ExternalSize = kv_external_size(KVs, NumDocs),
+            {NumDocs, ExternalSize};
+        (rereduce, Reds) ->
+            ExtractFun = fun(Red, {NumDocsAcc0, ExtAcc0}) ->
+                NumDocsAcc = NumDocsAcc0 + get_count(Red),
+                ExtAcc = ExtAcc0 + get_external_size_reds(Red),
+                {NumDocsAcc, ExtAcc}
+            end,
+            lists:foldl(ExtractFun, {0, 0}, Reds)
+    end.
+
 
 maybe_define_less_fun(#mrview{options = Options}) ->
     case couch_util:get_value(<<"collation">>, Options) of
diff --git a/src/couch_mrview/test/couch_mrview_map_views_tests.erl b/src/couch_mrview/test/couch_mrview_map_views_tests.erl
index 229af183d..805dc6c74 100644
--- a/src/couch_mrview/test/couch_mrview_map_views_tests.erl
+++ b/src/couch_mrview/test/couch_mrview_map_views_tests.erl
@@ -42,7 +42,8 @@ map_views_test_() ->
                     fun should_map_with_range/1,
                     fun should_map_with_limit_and_skip/1,
                     fun should_map_with_include_docs/1,
-                    fun should_map_empty_views/1
+                    fun should_map_empty_views/1,
+                    fun should_give_ext_size_seq_indexed_test/1
                 ]
             }
         }
@@ -118,6 +119,26 @@ should_map_empty_views(Db) ->
     ]},
     ?_assertEqual(Expect, Result).
 
+should_give_ext_size_seq_indexed_test(Db) ->
+    DDoc = couch_doc:from_json_obj({[
+        {<<"_id">>, <<"_design/seqdoc">>},
+        {<<"options">>, {[{<<"seq_indexed">>, true}]}},
+        {<<"views">>, {[
+                {<<"view1">>, {[
+                    {<<"map">>, <<"function(doc){emit(doc._id, doc._id);}">>}
+                ]}}
+            ]}
+        }
+    ]}),
+    {ok, _} = couch_db:update_doc(Db, DDoc, []),
+    {ok, Db1} = couch_db:open_int(couch_db:name(Db), []),
+    {ok, DDoc1} = couch_db:open_doc(Db1, <<"_design/seqdoc">>, [ejson_body]),
+    couch_mrview:query_view(Db1, DDoc1, <<"view1">>, [{update, true}]),
+    {ok, Info} = couch_mrview:get_info(Db1, DDoc),
+    Size = couch_util:get_nested_json_value({Info}, [sizes, external]),
+    ok = couch_db:close(Db1),
+    ?_assert(is_number(Size)).
+
 
 run_query(Db, Opts) ->
     couch_mrview:query_view(Db, <<"_design/bar">>, <<"baz">>, Opts).