fix: re-enable _doc_id & _design_docs filter optimisation paths (#1771)

3 files changed, 53 insertions, 17 deletions

diff --git a/src/couch/include/couch_db.hrl b/src/couch/include/couch_db.hrl
index feaa64069..801483aa1 100644
--- a/src/couch/include/couch_db.hrl
+++ b/src/couch/include/couch_db.hrl
@@ -203,6 +203,14 @@
     atts = []
 }).
 
+-record (fabric_changes_acc, {
+    db,
+    seq,
+    args,
+    options,
+    pending,
+    epochs
+}).
 
 -type doc() :: #doc{}.
 -type ddoc() :: #doc{}.
diff --git a/src/couch/src/couch_changes.erl b/src/couch/src/couch_changes.erl
index db465ee98..c5b5edf9f 100644
--- a/src/couch/src/couch_changes.erl
+++ b/src/couch/src/couch_changes.erl
@@ -24,7 +24,9 @@
     filter/3,
     handle_db_event/3,
     handle_view_event/3,
-    view_filter/3
+    view_filter/3,
+    send_changes_doc_ids/6,
+    send_changes_design_docs/6
 ]).
 
 -export([changes_enumerator/2]).
@@ -627,7 +629,14 @@ send_lookup_changes(FullDocInfos, StartSeq, Dir, Db, Fun, Acc0) ->
         {stop, Acc} -> Acc
     end,
     case Dir of
-        fwd -> {ok, FinalAcc#changes_acc{seq = couch_db:get_update_seq(Db)}};
+        fwd ->
+            FinalAcc0 = case element(1, FinalAcc) of
+                changes_acc -> % we came here via couch_http or internal call
+                    FinalAcc#changes_acc{seq = couch_db:get_update_seq(Db)};
+                fabric_changes_acc -> % we came here via chttpd / fabric / rexi
+                    FinalAcc#fabric_changes_acc{seq = couch_db:get_update_seq(Db)}
+            end,
+            {ok, FinalAcc0};
         rev -> {ok, FinalAcc}
     end.
 
diff --git a/src/fabric/src/fabric_rpc.erl b/src/fabric/src/fabric_rpc.erl
index c8aa19e0f..2b00a3668 100644
--- a/src/fabric/src/fabric_rpc.erl
+++ b/src/fabric/src/fabric_rpc.erl
@@ -32,15 +32,6 @@
 -include_lib("couch/include/couch_db.hrl").
 -include_lib("couch_mrview/include/couch_mrview.hrl").
 
--record (cacc, {
-    db,
-    seq,
-    args,
-    options,
-    pending,
-    epochs
-}).
-
 %% rpc endpoints
 %%  call to with_db will supply your M:F with a Db instance
 %%  and then remaining args
@@ -75,7 +66,7 @@ changes(DbName, Options, StartVector, DbOptions) ->
         StartSeq = calculate_start_seq(Db, node(), StartVector),
         Enum = fun changes_enumerator/2,
         Opts = [{dir,Dir}],
-        Acc0 = #cacc{
+        Acc0 = #fabric_changes_acc{
           db = Db,
           seq = StartSeq,
           args = Args,
@@ -84,8 +75,8 @@ changes(DbName, Options, StartVector, DbOptions) ->
           epochs = couch_db:get_epochs(Db)
         },
         try
-            {ok, #cacc{seq=LastSeq, pending=Pending, epochs=Epochs}} =
-                couch_db:fold_changes(Db, StartSeq, Enum, Acc0, Opts),
+            {ok, #fabric_changes_acc{seq=LastSeq, pending=Pending, epochs=Epochs}} =
+                do_changes(Db, StartSeq, Enum, Acc0, Opts),
             rexi:stream_last({complete, [
                 {seq, {LastSeq, uuid(Db), couch_db:owner_of(Epochs, LastSeq)}},
                 {pending, Pending}
@@ -97,6 +88,34 @@ changes(DbName, Options, StartVector, DbOptions) ->
         rexi:stream_last(Error)
     end.
 
+do_changes(Db, StartSeq, Enum, Acc0, Opts) ->
+    #fabric_changes_acc {
+        args = Args
+    } = Acc0,
+    #changes_args {
+        filter = Filter
+    } = Args,
+    case Filter of
+        "_doc_ids" ->
+            % optimised code path, we’re looking up all doc_ids in the by-id instead of filtering
+            % the entire by-seq tree to find the doc_ids one by one
+            #changes_args {
+                filter_fun = {doc_ids, Style, DocIds},
+                dir = Dir
+            } = Args,
+            couch_changes:send_changes_doc_ids(Db, StartSeq, Dir, Enum, Acc0, {doc_ids, Style, DocIds});
+        "_design_docs" ->
+            % optimised code path, we’re looking up all design_docs in the by-id instead of
+            % filtering the entire by-seq tree to find the design_docs one by one
+            #changes_args {
+                filter_fun = {design_docs, Style},
+                dir = Dir
+            } = Args,
+            couch_changes:send_changes_design_docs(Db, StartSeq, Dir, Enum, Acc0, {design_docs, Style});
+        _ ->
+            couch_db:fold_changes(Db, StartSeq, Enum, Acc0, Opts)
+    end.
+
 all_docs(DbName, Options, Args0) ->
     case fabric_util:upgrade_mrargs(Args0) of
         #mrargs{keys=undefined} = Args1 ->
@@ -482,9 +501,9 @@ reduce_cb(ok, ddoc_updated) ->
 changes_enumerator(#full_doc_info{} = FDI, Acc) ->
     changes_enumerator(couch_doc:to_doc_info(FDI), Acc);
 changes_enumerator(#doc_info{id= <<"_local/", _/binary>>, high_seq=Seq}, Acc) ->
-    {ok, Acc#cacc{seq = Seq, pending = Acc#cacc.pending-1}};
+    {ok, Acc#fabric_changes_acc{seq = Seq, pending = Acc#fabric_changes_acc.pending-1}};
 changes_enumerator(DocInfo, Acc) ->
-    #cacc{
+    #fabric_changes_acc{
         db = Db,
         args = #changes_args{
             include_docs = IncludeDocs,
@@ -513,7 +532,7 @@ changes_enumerator(DocInfo, Acc) ->
         ]}
     end,
     ok = rexi:stream2(ChangesRow),
-    {ok, Acc#cacc{seq = Seq, pending = Pending-1}}.
+    {ok, Acc#fabric_changes_acc{seq = Seq, pending = Pending-1}}.
 
 doc_member(Shard, DocInfo, Opts, Filter) ->
     case couch_db:open_doc(Shard, DocInfo, [deleted | Opts]) of