Add 'enable_session_registry' config

etc/emqx.conf

@@ -1898,6 +1898,11 @@ plugins.expand_plugins_dir = {{ platform_plugins_dir }}/
 ## Default: 1m, 1 minute
 broker.sys_interval = 1m
 
+## Enable global session registry.
+##
+## Value: on | off
+broker.enable_session_registry = on
+
 ## Session locking strategy in a cluster.
 ##
 ## Value: Enum

priv/emqx.schema

@@ -1723,6 +1723,11 @@ end}.
   {default, "1m"}
 ]}.
 
+{mapping, "broker.enable_session_registry", "emqx.enable_session_registry", [
+  {default, on},
+  {datatype, flag}
+]}.
+
 {mapping, "broker.session_locking_strategy", "emqx.session_locking_strategy", [
   {default, quorum},
   {datatype, {enum, [local,one,quorum,all]}}

src/emqx_sm_registry.erl

@@ -20,7 +20,6 @@
 
 -export([start_link/0]).
 -export([is_enabled/0]).
-
 -export([register_session/1, lookup_session/1, unregister_session/1]).
 
 %% gen_server callbacks
@@ -41,7 +40,8 @@ start_link() ->
     gen_server:start_link({local, ?REGISTRY}, ?MODULE, [], []).
 
 -spec(is_enabled() -> boolean()).
-is_enabled() -> ets:info(?TAB, name) =/= undefined.
+is_enabled() ->
+    emqx_config:get_env(enable_session_registry, true).
 
 -spec(lookup_session(emqx_types:client_id())
       -> list({emqx_types:client_id(), session_pid()})).
@@ -50,11 +50,17 @@ lookup_session(ClientId) ->
 
 -spec(register_session({emqx_types:client_id(), session_pid()}) -> ok).
 register_session({ClientId, SessPid}) when is_binary(ClientId), is_pid(SessPid) ->
-    mnesia:dirty_write(?TAB, record(ClientId, SessPid)).
+    case is_enabled() of
+        true -> mnesia:dirty_write(?TAB, record(ClientId, SessPid));
+        false -> ok
+    end.
 
 -spec(unregister_session({emqx_types:client_id(), session_pid()}) -> ok).
 unregister_session({ClientId, SessPid}) when is_binary(ClientId), is_pid(SessPid) ->
-    mnesia:dirty_delete_object(?TAB, record(ClientId, SessPid)).
+    case is_enabled() of
+        true -> mnesia:dirty_delete_object(?TAB, record(ClientId, SessPid));
+        false -> ok
+    end.
 
 record(ClientId, SessPid) ->
     #global_session{sid = ClientId, pid = SessPid}.