Merge pull request #14532 from rabbitmq/mergify/bp/v4.2.x/pr-14530

Optimise Khepri for concurrent reads (backport #14530)

Author: michaelklishin

deps/rabbit/src/rabbit_khepri.erl

@@ -1344,36 +1344,36 @@ register_rabbit_exchange_projection() ->
                     _VHost = ?KHEPRI_WILDCARD_STAR,
                     _Name = ?KHEPRI_WILDCARD_STAR),
     KeyPos = #exchange.name,
-    register_simple_projection(Name, PathPattern, KeyPos).
+    register_simple_projection(Name, PathPattern, KeyPos, true).
 
 register_rabbit_queue_projection() ->
     Name = rabbit_khepri_queue,
     PathPattern = rabbit_db_queue:khepri_queue_path(
                     _VHost = ?KHEPRI_WILDCARD_STAR,
                     _Name = ?KHEPRI_WILDCARD_STAR),
     KeyPos = 2, %% #amqqueue.name
-    register_simple_projection(Name, PathPattern, KeyPos).
+    register_simple_projection(Name, PathPattern, KeyPos, true).
 
 register_rabbit_vhost_projection() ->
     Name = rabbit_khepri_vhost,
     PathPattern = rabbit_db_vhost:khepri_vhost_path(
                     _VHost = ?KHEPRI_WILDCARD_STAR),
     KeyPos = 2, %% #vhost.virtual_host
-    register_simple_projection(Name, PathPattern, KeyPos).
+    register_simple_projection(Name, PathPattern, KeyPos, false).
 
 register_rabbit_users_projection() ->
     Name = rabbit_khepri_user,
     PathPattern = rabbit_db_user:khepri_user_path(
                     _UserName = ?KHEPRI_WILDCARD_STAR),
     KeyPos = 2, %% #internal_user.username
-    register_simple_projection(Name, PathPattern, KeyPos).
+    register_simple_projection(Name, PathPattern, KeyPos, false).
 
 register_rabbit_global_runtime_parameters_projection() ->
     Name = rabbit_khepri_global_rtparam,
     PathPattern = rabbit_db_rtparams:khepri_global_rp_path(
                     _Key = ?KHEPRI_WILDCARD_STAR_STAR),
     KeyPos = #runtime_parameters.key,
-    register_simple_projection(Name, PathPattern, KeyPos).
+    register_simple_projection(Name, PathPattern, KeyPos, false).
 
 register_rabbit_per_vhost_runtime_parameters_projection() ->
     Name = rabbit_khepri_per_vhost_rtparam,
@@ -1382,18 +1382,19 @@ register_rabbit_per_vhost_runtime_parameters_projection() ->
                     _Component = ?KHEPRI_WILDCARD_STAR_STAR,
                     _Name = ?KHEPRI_WILDCARD_STAR_STAR),
     KeyPos = #runtime_parameters.key,
-    register_simple_projection(Name, PathPattern, KeyPos).
+    register_simple_projection(Name, PathPattern, KeyPos, false).
 
 register_rabbit_user_permissions_projection() ->
     Name = rabbit_khepri_user_permission,
     PathPattern = rabbit_db_user:khepri_user_permission_path(
                     _UserName = ?KHEPRI_WILDCARD_STAR,
                     _VHost = ?KHEPRI_WILDCARD_STAR),
     KeyPos = #user_permission.user_vhost,
-    register_simple_projection(Name, PathPattern, KeyPos).
+    register_simple_projection(Name, PathPattern, KeyPos, false).
 
-register_simple_projection(Name, PathPattern, KeyPos) ->
-    Options = #{keypos => KeyPos},
+register_simple_projection(Name, PathPattern, KeyPos, ReadConcurrency) ->
+    Options = #{keypos => KeyPos,
+                read_concurrency => ReadConcurrency},
     Projection = khepri_projection:new(Name, copy, Options),
     khepri:register_projection(?STORE_ID, PathPattern, Projection).
 
@@ -1429,7 +1430,9 @@ register_rabbit_index_route_projection() ->
                                   destination = Destination}
              end,
     ProjectionFun = projection_fun_for_sets(MapFun),
-    Options = #{type => bag, keypos => #index_route.source_key},
+    Options = #{type => bag,
+                keypos => #index_route.source_key,
+                read_concurrency => true},
     Projection = khepri_projection:new(
                    rabbit_khepri_index_route, ProjectionFun, Options),
     DirectOrFanout = #if_data_matches{
@@ -1497,7 +1500,8 @@ register_rabbit_topic_graph_projection() ->
     end,
     Options = #{keypos => #topic_trie_edge.trie_edge,
                 standalone_fun_options =>
-                #{should_process_function => ShouldProcessFun}},
+                #{should_process_function => ShouldProcessFun},
+                read_concurrency => true},
     ProjectionFun =
     fun(Table, Path, OldProps, NewProps) ->
         {