projections: Refactor rabbit_khepri_bindings table layout

The old shape used the source exchange as the key in a bag table. This
made it cheaper to list all bindings for an exchange but it caused a
bad regression for inserting many bindings, for example in a definition
import. If all bindings are for the same exchange, inserting N bindings
has exponential time complexity when using a bag compared to the
roughly linear time complexity using a set.

This reflects the shape of the `rabbit_route` table from mnesia: the
whole `#binding{}` record is the key of the table and the table is
a set. With this change, the time taken to import definitions roughly
matches mnesia.

2 files changed, 21 insertions, 17 deletions

diff --git a/deps/rabbit/src/rabbit_db_binding.erl b/deps/rabbit/src/rabbit_db_binding.erl
index 3e3779bb92..b75fdf4f9f 100644
--- a/deps/rabbit/src/rabbit_db_binding.erl
+++ b/deps/rabbit/src/rabbit_db_binding.erl
@@ -431,10 +431,11 @@ get_all_in_mnesia(VHost) ->
     [B || #route{binding = B} <- rabbit_db:list_in_mnesia(?MNESIA_TABLE, Match)].
 
 get_all_in_khepri(VHost) ->
-    Path = khepri_routes_path() ++ [VHost, rabbit_khepri:if_has_data_wildcard()],
-    lists:foldl(fun(SetOfBindings, Acc) ->
-                        sets:to_list(SetOfBindings) ++ Acc
-                end, [], rabbit_db:list_in_khepri(Path)).
+    VHostResource = rabbit_misc:r(VHost, '_'),
+    Match = #route{binding = #binding{source      = VHostResource,
+                                      destination = VHostResource,
+                                      _           = '_'}},
+    [B || #route{binding = B} <- ets:match_object(rabbit_khepri_bindings, Match)].
 
 -spec get_all(Src, Dst, Reverse) -> [Binding] when
       Src :: rabbit_types:binding_source(),
@@ -462,10 +463,10 @@ get_all_in_mnesia(SrcName, DstName, Reverse) ->
     mnesia:async_dirty(Fun).
 
 get_all_in_khepri(SrcName, DstName) ->
-    Match = #binding{source      = SrcName,
-                     destination = DstName,
-                     _           = '_'},
-    ets:match_object(rabbit_khepri_bindings, Match).
+    MatchHead = #route{binding = #binding{source      = SrcName,
+                                          destination = DstName,
+                                          _           = '_'}},
+    [B || #route{binding = B} <- ets:match_object(rabbit_khepri_bindings, MatchHead)].
 
 %% -------------------------------------------------------------------
 %% get_all_for_source().
@@ -504,7 +505,8 @@ list_for_route(Route, true) ->
     end.
 
 get_all_for_source_in_khepri(Resource) ->
-    ets:lookup(rabbit_khepri_bindings, Resource).
+    Route = #route{binding = #binding{source = Resource, _ = '_'}},
+    [B || #route{binding = B} <- ets:match_object(rabbit_khepri_bindings, Route)].
 
 %% -------------------------------------------------------------------
 %% get_all_for_destination().
@@ -533,10 +535,10 @@ get_all_for_destination_in_mnesia(Dst) ->
     mnesia:async_dirty(Fun).
 
 get_all_for_destination_in_khepri(Destination) ->
-     %% TODO: projection for bindings indexed by destination?
-    Match = #binding{destination = Destination,
-                     _           = '_'},
-    ets:match_object(rabbit_khepri_bindings, Match).
+    %% TODO: projection for bindings indexed by destination?
+    Match = #route{binding = #binding{destination = Destination,
+                                      _           = '_'}},
+    [B || #route{binding = B} <- ets:match_object(rabbit_khepri_bindings, Match)].
 
 %% -------------------------------------------------------------------
 %% fold().
@@ -609,8 +611,10 @@ match_in_mnesia(SrcName, Match) ->
                  Routes, Match(Binding)].
 
 match_in_khepri(SrcName, Match) ->
-    Routes = ets:lookup(rabbit_khepri_bindings, SrcName),
-    [Dest || Binding = #binding{destination = Dest} <-
+    MatchHead = #route{binding = #binding{source      = SrcName,
+                                          _           = '_'}},
+    Routes = ets:select(rabbit_khepri_bindings, [{MatchHead, [], [['$_']]}]),
+    [Dest || [#route{binding = Binding = #binding{destination = Dest}}] <-
                  Routes, Match(Binding)].
 
 %% Routing - HOT CODE PATH
diff --git a/deps/rabbit/src/rabbit_khepri.erl b/deps/rabbit/src/rabbit_khepri.erl
index fb1a4ea8cd..1c11dd1edd 100644
--- a/deps/rabbit/src/rabbit_khepri.erl
+++ b/deps/rabbit/src/rabbit_khepri.erl
@@ -654,10 +654,10 @@ register_simple_projection(Name, PathPattern, KeyPos) ->
 
 register_rabbit_bindings_projection() ->
     MapFun = fun(_Path, Binding) ->
-                     Binding
+                     #route{binding = Binding}
              end,
     ProjectionFun = projection_fun_for_sets(MapFun),
-    Options = #{type => bag, keypos => #binding.source},
+    Options = #{keypos => #route.binding},
     Projection = khepri_projection:new(
                    rabbit_khepri_bindings, ProjectionFun, Options),
     PathPattern = [rabbit_db_binding,