[GitHub] [couchdb] davisp commented on a change in pull request #2869: fetch local docs in fold_docs function

[GitBox <gi...@apache.org>]

davisp commented on a change in pull request #2869:
URL: https://github.com/apache/couchdb/pull/2869#discussion_r420246021



##########
File path: src/fabric/src/fabric2_db.erl
##########
@@ -996,17 +996,32 @@ fold_docs(Db, DocIds, UserFun, UserAcc0, Options) ->
                 user_fun => UserFun
             },
 
-            FinalAcc1 = lists:foldl(fun(DocId, Acc) ->
-                #{
-                    revs_q := RevsQ,
-                    revs_count := RevsCount
-                } = Acc,
-                Future = FetchRevs(DocId),
-                NewAcc = Acc#{
-                    revs_q := queue:in({DocId, Future}, RevsQ),
-                    revs_count := RevsCount + 1
-                },
-                drain_fold_docs_revs_futures(TxDb, NewAcc)
+            FinalAcc1 = lists:foldl(fun
+                (<<?LOCAL_DOC_PREFIX, _/binary>> = DocId, Acc) ->
+                    DocResp = case fabric2_fdb:get_local_doc(TxDb, DocId) of
+                        #doc{} = Doc -> {ok, Doc};
+                        _Else -> {not_found, missing}
+                    end,
+                    #{
+                        user_acc := UserAcc,
+                        user_fun := UserFun
+                    } = Acc,
+
+                    NewUserAcc = maybe_stop(UserFun(DocId, DocResp, UserAcc)),

Review comment:
       This is broken. You can't mix synchronous and asynchronous fetches like this. `POST /dbname/_all_docs` has a (perhaps implicit?) contract for returning docs in the order specified in the body. Mixing these operations means that we'd be returning any `_local` docs in some random position within the previous 100 or so docs returned.




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