feat(ds): Dynamic backend registration

apps/emqx_durable_storage/src/emqx_ds.erl

@@ -23,8 +23,10 @@
 
 %% Management API:
 -export([
-    base_dir/0,
+    register_backend/2,
+
     open_db/2,
+    close_db/1,
     update_db_config/2,
     add_generation/1,
     list_generations_with_lifetimes/1,
@@ -199,6 +201,8 @@
 
 -callback open_db(db(), create_db_opts()) -> ok | {error, _}.
 
+-callback close_db(db()) -> ok.
+
 -callback add_generation(db()) -> ok | {error, _}.
 
 -callback update_db_config(db(), create_db_opts()) -> ok | {error, _}.
@@ -247,21 +251,26 @@
 %% API functions
 %%================================================================================
 
--spec base_dir() -> file:filename().
-base_dir() ->
-    application:get_env(?APP, db_data_dir, emqx:data_dir()).
+%% @doc Register DS backend.
+-spec register_backend(atom(), module()) -> ok.
+register_backend(Name, Module) ->
+    persistent_term:put({emqx_ds_backend_module, Name}, Module).
 
 %% @doc Different DBs are completely independent from each other. They
 %% could represent something like different tenants.
 -spec open_db(db(), create_db_opts()) -> ok.
-open_db(DB, Opts = #{backend := Backend}) when Backend =:= builtin orelse Backend =:= fdb ->
-    Module =
-        case Backend of
-            builtin -> emqx_ds_replication_layer;
-            fdb -> emqx_fdb_ds
-        end,
-    persistent_term:put(?persistent_term(DB), Module),
-    ?module(DB):open_db(DB, Opts).
+open_db(DB, Opts = #{backend := Backend}) ->
+    case persistent_term:get({emqx_ds_backend_module, Backend}, undefined) of
+        undefined ->
+            error({no_such_backend, Backend});
+        Module ->
+            persistent_term:put(?persistent_term(DB), Module),
+            ?module(DB):open_db(DB, Opts)
+    end.
+
+-spec close_db(db()) -> ok.
+close_db(DB) ->
+    ?module(DB):close_db(DB).
 
 -spec add_generation(db()) -> ok.
 add_generation(DB) ->

apps/emqx_durable_storage/src/emqx_ds_storage_layer.erl

@@ -55,7 +55,7 @@
 -export([init/1, format_status/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2]).
 
 %% internal exports:
--export([db_dir/1]).
+-export([db_dir/1, base_dir/0]).
 
 -export_type([
     gen_id/0,
@@ -889,13 +889,17 @@ rocksdb_open(Shard, Options) ->
             Error
     end.
 
+-spec base_dir() -> file:filename().
+base_dir() ->
+    application:get_env(?APP, db_data_dir, emqx:data_dir()).
+
 -spec db_dir(shard_id()) -> file:filename().
 db_dir({DB, ShardId}) ->
-    filename:join([emqx_ds:base_dir(), DB, binary_to_list(ShardId)]).
+    filename:join([base_dir(), DB, binary_to_list(ShardId)]).
 
 -spec checkpoints_dir(shard_id()) -> file:filename().
 checkpoints_dir({DB, ShardId}) ->
-    filename:join([emqx_ds:base_dir(), DB, checkpoints, binary_to_list(ShardId)]).
+    filename:join([base_dir(), DB, checkpoints, binary_to_list(ShardId)]).
 
 -spec checkpoint_dir(shard_id(), _Name :: file:name()) -> file:filename().
 checkpoint_dir(ShardId, Name) ->