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Replace Khepri topic routing projection with trie + ordered_set (v4) #15619

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Merged
ansd merged 2 commits into from
Apr 9, 2026
Merged

Replace Khepri topic routing projection with trie + ordered_set (v4) #15619

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e977475
Replace Khepri topic routing projection with trie + ordered_set (v4)
ansd Mar 3, 2026
623a2f2
Improve function names
ansd Apr 9, 2026
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11 changes: 11 additions & 0 deletions deps/rabbit/src/rabbit_core_ff.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -244,3 +244,14 @@
{rabbit_db_queue,
tie_binding_to_dest_with_keep_while_cond_enable}}
}}).

-rabbit_feature_flag(
{topic_binding_projection_v4,
#{desc => "Enable the topic binding Khepri projection v4",
stability => stable,
depends_on => ['rabbitmq_4.3.0'],
callbacks => #{enable =>
{rabbit_khepri, topic_binding_projection_enable},
post_enable =>
{rabbit_khepri, topic_binding_projection_post_enable}}
}}).
213 changes: 160 additions & 53 deletions deps/rabbit/src/rabbit_db_topic_exchange.erl
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,10 @@
%% Used by Khepri projections and the Mnesia-to-Khepri migration.
-export([split_topic_key_binary/1]).

-define(KHEPRI_PROJECTION, rabbit_khepri_topic_trie_v3).
-define(KHEPRI_PROJECTION_V3, rabbit_khepri_topic_trie_v3).

-define(TOPIC_TRIE_PROJECTION, rabbit_khepri_topic_trie_v4).
-define(TOPIC_BINDING_PROJECTION, rabbit_khepri_topic_binding_v4).

-type match_result() :: [rabbit_types:binding_destination() |
{rabbit_amqqueue:name(), rabbit_types:binding_key()}].
Expand All @@ -31,14 +34,20 @@
%%
%% @private

match(XName, RoutingKey, Opts) ->
match(#resource{virtual_host = VHost, name = XName} = X, RoutingKey, Opts) ->
BKeys = maps:get(return_binding_keys, Opts, false),
Words = split_topic_key_binary(RoutingKey),
trie_match_in_khepri(XName, Words, BKeys).

%% --------------------------------------------------------------
%% split_topic_key_binary().
%% --------------------------------------------------------------
case rabbit_khepri:get_effective_topic_binding_projection_version() of
V when V >= 4 ->
try
trie_match({VHost, XName}, root, Words, BKeys, [])
catch
error:badarg ->
[]
end;
_ ->
trie_match_v3(X, Words, BKeys)
end.

-spec split_topic_key_binary(RoutingKey) -> Words when
RoutingKey :: binary(),
Expand All @@ -58,81 +67,164 @@ split_topic_key_binary(RoutingKey) ->
end,
binary:split(RoutingKey, Pattern, [global]).

%% --------------------------------------------------------------
%% Internal
%% --------------------------------------------------------------
%% ==============================================================
%% Trie-based routing
%%
%% Uses two ETS tables:
%%
%% 1. Trie edges table (set): {Key, ChildNodeId, ChildCount}
%% Key = {XSrc, ParentNodeId, Word}
%% Navigation: ets:lookup_element/4 for O(1) edge traversal.
%%
%% 2. Leaf bindings table (ordered_set): {{NodeId, BindingKey, Dest}}
%% Collection: ets:next/2 probes for fanout 0-2 (fast path), then
%% ets:select/2 with a partially bound key for fanout > 2 (does an
%% O(log N) seek followed by O(F) range scan).
%%
%% Routing walks the trie (branching on literal word, <<"*">>, <<"#">>)
%% then collects destinations from the bindings table at each matching
%% leaf. This is O(depth * 3) for the trie walk, plus O(log N) per
%% leaf for fanout 0-2, or O(log N + F) per leaf for fanout F > 2.
%% ==============================================================

-spec add_matched([rabbit_types:binding_destination() |
{rabbit_types:binding_destination(), BindingArgs :: list()}],
ReturnBindingKeys :: boolean(),
match_result()) ->
match_result().
add_matched(Destinations, false, Acc) ->
Destinations ++ Acc;
add_matched(DestinationsArgs, true, Acc) ->
lists:foldl(
fun({DestQ = #resource{kind = queue}, BindingArgs}, L) ->
case rabbit_misc:table_lookup(BindingArgs, <<"x-binding-key">>) of
{longstr, BKey} ->
[{DestQ, BKey} | L];
_ ->
[DestQ | L]
end;
({DestX, _BindingArgs}, L) ->
[DestX | L]
end, Acc, DestinationsArgs).
trie_match(XSrc, Node, [], BKeys, Acc0) ->
Acc1 = trie_bindings(Node, BKeys, Acc0),
trie_match_try(XSrc, Node, <<"#">>,
fun trie_match_skip_any/5,
[], BKeys, Acc1);
trie_match(XSrc, Node, [W | RestW] = Words, BKeys, Acc0) ->
Acc1 = trie_match_try(XSrc, Node, W,
fun trie_match/5,
RestW, BKeys, Acc0),
Acc2 = trie_match_try(XSrc, Node, <<"*">>,
fun trie_match/5,
RestW, BKeys, Acc1),
trie_match_try(XSrc, Node, <<"#">>,
fun trie_match_skip_any/5,
Words, BKeys, Acc2).

trie_match_try(XSrc, Node, Word, MatchFun, RestW, BKeys, Acc) ->
case ets:lookup_element(?TOPIC_TRIE_PROJECTION,
{XSrc, Node, Word}, 2, undefined) of
undefined ->
Acc;
NextNode ->
MatchFun(XSrc, NextNode, RestW, BKeys, Acc)
end.

%% Khepri topic graph
trie_match_skip_any(XSrc, Node, [], BKeys, Acc) ->
trie_match(XSrc, Node, [], BKeys, Acc);
trie_match_skip_any(XSrc, Node, [_ | RestW] = Words, BKeys, Acc) ->
trie_match_skip_any(
XSrc, Node, RestW, BKeys,
trie_match(XSrc, Node, Words, BKeys, Acc)).

trie_match_in_khepri(X, Words, BKeys) ->
%% Collect all destinations bound at the given trie node.
%%
%% Uses ets:next/2 for up to two elements (fast path for the common
%% fanout 0-2 cases), then switches to ets:select/2 when fanout > 2.
%%
%% ets:select/2 occurs the expensive match spec compilation overhead.
%% For larger fanouts, the cost for compiling the match spec amortises.
%% ets:select/2 occurs an O(log N) seek followed by an O(F) range scan,
%% which is cheaper than F individual ets:next/2 calls
%% (each O(log N) due to CATree fresh-stack allocation).
trie_bindings(NodeId, BKeys, Acc) ->
StartKey = {NodeId, <<>>, {}},
case ets:next(?TOPIC_BINDING_PROJECTION, StartKey) of
{NodeId, BKey1, Dest1} = Key1 ->
case ets:next(?TOPIC_BINDING_PROJECTION, Key1) of
{NodeId, BKey2, Dest2} = Key2 ->
case ets:next(?TOPIC_BINDING_PROJECTION, Key2) of
{NodeId, _, _} ->
collect_select(NodeId, BKeys, Acc);
_ ->
Acc1 = collect_binding(Dest1, BKey1, BKeys, Acc),
collect_binding(Dest2, BKey2, BKeys, Acc1)
end;
_ ->
collect_binding(Dest1, BKey1, BKeys, Acc)
end;
_ ->
Acc
end.

collect_binding(#resource{kind = queue} = Dest, BindingKey, true, Acc) ->
[{Dest, BindingKey} | Acc];
collect_binding(Dest, _BindingKey, _ReturnBindingKeys, Acc) ->
[Dest | Acc].

collect_select(NodeId, false, Acc) ->
Dests = ets:select(?TOPIC_BINDING_PROJECTION,
[{{{NodeId, '_', '$1'}}, [], ['$1']}]),
Dests ++ Acc;
collect_select(NodeId, true, Acc) ->
DestsAndBKeys = ets:select(?TOPIC_BINDING_PROJECTION,
[{{{NodeId, '$1', '$2'}}, [], [{{'$2', '$1'}}]}]),
format_dest_bkeys(DestsAndBKeys, Acc).

format_dest_bkeys([], Acc) ->
Acc;
format_dest_bkeys([{#resource{kind = queue} = Dest, BKey} | Rest], Acc) ->
format_dest_bkeys(Rest, [{Dest, BKey} | Acc]);
format_dest_bkeys([{Dest, _BKey} | Rest], Acc) ->
format_dest_bkeys(Rest, [Dest | Acc]).

%% ==============================================================
%% Old v3 Khepri topic graph.
%% Delete these *_v3 functions when feature flag
%% topic_binding_projection_v4 becomes required.
%% ==============================================================

trie_match_v3(X, Words, BKeys) ->
try
trie_match_in_khepri(X, root, Words, BKeys, [])
trie_match_v3(X, root, Words, BKeys, [])
catch
error:badarg ->
[]
end.

trie_match_in_khepri(X, Node, [], BKeys, ResAcc0) ->
Destinations = trie_bindings_in_khepri(X, Node, BKeys),
ResAcc = add_matched(Destinations, BKeys, ResAcc0),
trie_match_part_in_khepri(
trie_match_v3(X, Node, [], BKeys, ResAcc0) ->
Destinations = trie_bindings_v3(X, Node, BKeys),
ResAcc = add_matched_v3(Destinations, BKeys, ResAcc0),
trie_match_part_v3(
X, Node, <<"#">>,
fun trie_match_skip_any_in_khepri/5, [], BKeys, ResAcc);
trie_match_in_khepri(X, Node, [W | RestW] = Words, BKeys, ResAcc) ->
fun trie_match_skip_any_v3/5, [], BKeys, ResAcc);
trie_match_v3(X, Node, [W | RestW] = Words, BKeys, ResAcc) ->
lists:foldl(fun ({WArg, MatchFun, RestWArg}, Acc) ->
trie_match_part_in_khepri(
trie_match_part_v3(
X, Node, WArg, MatchFun, RestWArg, BKeys, Acc)
end, ResAcc, [{W, fun trie_match_in_khepri/5, RestW},
{<<"*">>, fun trie_match_in_khepri/5, RestW},
end, ResAcc, [{W, fun trie_match_v3/5, RestW},
{<<"*">>, fun trie_match_v3/5, RestW},
{<<"#">>,
fun trie_match_skip_any_in_khepri/5, Words}]).
fun trie_match_skip_any_v3/5, Words}]).

trie_match_part_in_khepri(X, Node, Search, MatchFun, RestW, BKeys, ResAcc) ->
case trie_child_in_khepri(X, Node, Search) of
trie_match_part_v3(X, Node, Search, MatchFun, RestW, BKeys, ResAcc) ->
case trie_child_v3(X, Node, Search) of
{ok, NextNode} -> MatchFun(X, NextNode, RestW, BKeys, ResAcc);
error -> ResAcc
end.

trie_match_skip_any_in_khepri(X, Node, [], BKeys, ResAcc) ->
trie_match_in_khepri(X, Node, [], BKeys, ResAcc);
trie_match_skip_any_in_khepri(X, Node, [_ | RestW] = Words, BKeys, ResAcc) ->
trie_match_skip_any_in_khepri(
trie_match_skip_any_v3(X, Node, [], BKeys, ResAcc) ->
trie_match_v3(X, Node, [], BKeys, ResAcc);
trie_match_skip_any_v3(X, Node, [_ | RestW] = Words, BKeys, ResAcc) ->
trie_match_skip_any_v3(
X, Node, RestW, BKeys,
trie_match_in_khepri(X, Node, Words, BKeys, ResAcc)).
trie_match_v3(X, Node, Words, BKeys, ResAcc)).

trie_child_in_khepri(X, Node, Word) ->
trie_child_v3(X, Node, Word) ->
case ets:lookup(
?KHEPRI_PROJECTION,
?KHEPRI_PROJECTION_V3,
#trie_edge{exchange_name = X,
node_id = Node,
word = Word}) of
[#topic_trie_edge_v2{node_id = NextNode}] -> {ok, NextNode};
[] -> error
end.

trie_bindings_in_khepri(X, Node, BKeys) ->
trie_bindings_v3(X, Node, BKeys) ->
case ets:lookup(
?KHEPRI_PROJECTION,
?KHEPRI_PROJECTION_V3,
#trie_edge{exchange_name = X,
node_id = Node,
word = bindings}) of
Expand All @@ -147,3 +239,18 @@ trie_bindings_in_khepri(X, Node, BKeys) ->
[] ->
[]
end.

add_matched_v3(Destinations, false, Acc) ->
Destinations ++ Acc;
add_matched_v3(DestinationsArgs, true, Acc) ->
lists:foldl(
fun({DestQ = #resource{kind = queue}, BindingArgs}, L) ->
case rabbit_misc:table_lookup(BindingArgs, <<"x-binding-key">>) of
{longstr, BKey} ->
[{DestQ, BKey} | L];
_ ->
[DestQ | L]
end;
({DestX, _BindingArgs}, L) ->
[DestX | L]
end, Acc, DestinationsArgs).
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