feat(ds): Support metrics for builtin_local backend

apps/emqx/test/emqx_persistent_messages_SUITE.erl

@@ -33,7 +33,12 @@ all() ->
     emqx_common_test_helpers:all(?MODULE).
 
 init_per_suite(Config) ->
-    Config.
+    case is_standalone() of
+        true ->
+            {skip, standalone_not_supported};
+        false ->
+            Config
+    end.
 
 end_per_suite(_Config) ->
     ok.
@@ -590,3 +595,11 @@ on_message_dropped(Msg, Context, Res, TestPid) ->
     ErrCtx = #{msg => Msg, ctx => Context, res => Res},
     ct:pal("this hook should not be called.\n  ~p", [ErrCtx]),
     exit(TestPid, {hookpoint_called, ErrCtx}).
+
+is_standalone() ->
+    try
+        emqx_conf:module_info(),
+        false
+    catch
+        error:undef -> true
+    end.

apps/emqx_durable_storage/src/emqx_ds.erl

@@ -27,6 +27,7 @@
 
     open_db/2,
     close_db/1,
+    which_dbs/0,
     update_db_config/2,
     add_generation/1,
     list_generations_with_lifetimes/1,
@@ -264,13 +265,19 @@ open_db(DB, Opts = #{backend := Backend}) ->
             error({no_such_backend, Backend});
         Module ->
             persistent_term:put(?persistent_term(DB), Module),
+            emqx_ds_sup:register_db(DB, Backend),
             ?module(DB):open_db(DB, Opts)
     end.
 
 -spec close_db(db()) -> ok.
 close_db(DB) ->
+    emqx_ds_sup:unregister_db(DB),
     ?module(DB):close_db(DB).
 
+-spec which_dbs() -> [{db(), _Backend :: atom()}].
+which_dbs() ->
+    emqx_ds_sup:which_dbs().
+
 -spec add_generation(db()) -> ok.
 add_generation(DB) ->
     ?module(DB):add_generation(DB).

apps/emqx_durable_storage/src/emqx_ds_buffer.erl

@@ -39,7 +39,8 @@
 %% Type declarations
 %%================================================================================
 
--define(via(DB, Shard), {via, gproc, {n, l, {?MODULE, DB, Shard}}}).
+-define(name(DB, SHARD), {n, l, {?MODULE, DB, SHARD}}).
+-define(via(DB, SHARD), {via, gproc, ?name(DB, SHARD)}).
 -define(flush, flush).
 
 -define(cbm(DB), {?MODULE, DB}).
@@ -66,7 +67,7 @@
 
 -spec ls() -> [{emqx_ds:db(), _Shard}].
 ls() ->
-    MS = {{n, l, {?MODULE, '$1', '$2'}}, [], ['$1', '$2']},
+    MS = {{?name('$1', '$2'), '_', '_'}, [], [{{'$1', '$2'}}]},
     gproc:select({local, names}, [MS]).
 
 -spec start_link(module(), _CallbackOptions, emqx_ds:db(), _ShardId) ->

apps/emqx_durable_storage/src/emqx_ds_builtin_metrics.erl

@@ -176,11 +176,14 @@ prometheus_collect(NodeOrAggr) ->
 
 prometheus_per_db(NodeOrAggr) ->
     lists:foldl(
-        fun(DB, Acc) ->
-            prometheus_per_db(NodeOrAggr, DB, Acc)
+        fun
+            ({DB, Backend}, Acc) when Backend =:= builtin_local; Backend =:= builtin_raft ->
+                prometheus_per_db(NodeOrAggr, DB, Acc);
+            ({_, _}, Acc) ->
+                Acc
         end,
         #{},
-        emqx_ds_builtin_raft_db_sup:which_dbs()
+        emqx_ds:which_dbs()
     ).
 
 %% This function returns the data in the following format:
@@ -235,18 +238,15 @@ prometheus_per_db(NodeOrAggr, DB, Acc0) ->
 %% If `NodeOrAggr' = `node' then node name is appended to the list of
 %% labels.
 prometheus_per_shard(NodeOrAggr) ->
+    prometheus_buffer_metrics(NodeOrAggr).
+
+prometheus_buffer_metrics(NodeOrAggr) ->
     lists:foldl(
-        fun(DB, Acc0) ->
-            lists:foldl(
-                fun(Shard, Acc) ->
-                    prometheus_per_shard(NodeOrAggr, DB, Shard, Acc)
-                end,
-                Acc0,
-                emqx_ds_replication_layer_meta:shards(DB)
-            )
+        fun({DB, Shard}, Acc) ->
+            prometheus_per_shard(NodeOrAggr, DB, Shard, Acc)
         end,
         #{},
-        emqx_ds_builtin_raft_db_sup:which_dbs()
+        emqx_ds_buffer:ls()
     ).
 
 prometheus_per_shard(NodeOrAggr, DB, Shard, Acc0) ->

apps/emqx_durable_storage/src/emqx_ds_sup.erl

@@ -19,6 +19,7 @@
 
 %% API:
 -export([start_link/0, attach_backend/2]).
+-export([register_db/2, unregister_db/1, which_dbs/0]).
 
 %% behaviour callbacks:
 -export([init/1]).
@@ -28,6 +29,7 @@
 %%================================================================================
 
 -define(SUP, ?MODULE).
+-define(TAB, ?MODULE).
 
 %%================================================================================
 %% API functions
@@ -58,11 +60,23 @@ attach_backend(Backend, Start) ->
             {error, Err}
     end.
 
+register_db(DB, Backend) ->
+    ets:insert(?TAB, {DB, Backend}),
+    ok.
+
+unregister_db(DB) ->
+    ets:delete(?TAB, DB),
+    ok.
+
+which_dbs() ->
+    ets:tab2list(?TAB).
+
 %%================================================================================
 %% behaviour callbacks
 %%================================================================================
 
 init(top) ->
+    _ = ets:new(?TAB, [public, set, named_table]),
     Children = [],
     SupFlags = #{
         strategy => one_for_one,