Initialize external backends earlier to allow backup and fallback to work

lib/mnesia/src/mnesia_bup.erl

@@ -83,7 +83,18 @@ iterate(Mod, Fun, Opaque, Acc) ->
     R = #restore{bup_module = Mod, bup_data = Opaque},
     try read_schema_section(R) of
 	{R2, {Header, Schema, Rest}} ->
-            Ext = get_ext_types(Schema),
+        Ext = get_ext_types(Schema),
+        case mnesia:system_info(is_running) of
+            Status when Status == yes orelse Status == starting ->
+                dbg_out("Status is ~p, initializing external backends.~n", [Status]),
+                Backends = mnesia_schema:get_backends_to_initialize(Ext),
+                mnesia_schema:init_backends(Backends);
+            Status ->
+                %% Do not initialize external backends if the system is not running
+                %% We can land here, if system is stopped and we're creating a schema
+                %% this triggers an implicit backup and fallback install
+                dbg_out("Status is ~p, skipping external backends initialization.~n", [Status])
+        end,
 	    try iter(R2, Header, Schema, Ext, Fun, Acc, Rest) of
 		{ok, R3, Res} ->
 		    close_read(R3),
@@ -745,12 +756,12 @@ do_fallback_start(true, false) ->
             ?SAFE(dets:close(schema)),
             TmpSchema = mnesia_lib:tab2tmp(schema),
             DatSchema = mnesia_lib:tab2dat(schema),
-	    AllLT  = ?ets_match_object(LocalTabs, '_'),
-	    ?ets_delete_table(LocalTabs),
+            AllLT  = ?ets_match_object(LocalTabs, '_'),
+            ?ets_delete_table(LocalTabs),
             case file:rename(TmpSchema, DatSchema) of
                 ok ->
-		    [(LT#local_tab.swap)(LT#local_tab.name, LT) ||
-			LT <- AllLT, LT#local_tab.name =/= schema],
+                    [(LT#local_tab.swap)(LT#local_tab.name, LT) ||
+                    LT <- AllLT, LT#local_tab.name =/= schema],
                     file:delete(BupFile),
                     ok;
                 {error, Reason} ->

lib/mnesia/src/mnesia_lib.erl

@@ -432,6 +432,7 @@ validate_record(Tab, Obj) ->
 %%
 %%   dir                                  -> directory path (**)
 %%   mnesia_status                        -> status | running | stopping (**)
+%%   ext_backends                         -> module list of initialized ext backends (**)
 %%   (**) ==   (Different on all nodes)
 %%
 
@@ -458,6 +459,7 @@ other_val_1(Var) ->
 	{_, where_to_read} -> nowhere;
 	{_, where_to_write} -> [];
 	{_, active_replicas} -> [];
+	ext_backends -> [];
 	_ -> error
     end.
 

lib/mnesia/src/mnesia_schema.erl

@@ -72,6 +72,8 @@
          info/1,
          init/1,
 	 init_backends/0,
+	 init_backends/1,
+	 get_backends_to_initialize/1,
          insert_cstruct/3,
 	 is_remote_member/1,
          list2cs/1,
@@ -161,13 +163,22 @@ init(IgnoreFallback) ->
     mnesia_controller:add_active_replica(schema, node()),
     init_backends().
 
-
 init_backends() ->
-    Backends = lists:foldl(fun({Alias, Mod}, Acc) ->
-				   orddict:append(Mod, Alias, Acc)
-			   end, orddict:new(), get_ext_types()),
-    [init_backend(Mod, Aliases) || {Mod, Aliases} <- Backends],
-    ok.
+    Backends = get_backends_to_initialize(get_ext_types()),
+    init_backends(Backends).
+init_backends([]) ->
+    ok;
+init_backends([{Mod, Aliases} = Backend | Rest]) ->
+    Mods = mnesia_lib:val(ext_backends),
+    case lists:member(Mod, Mods) of
+        true ->
+            dbg_out("Backend ~p is already initialized~n", [Backend]);
+        false ->
+            init_backend(Mod, Aliases),
+            mnesia_lib:set(ext_backends, [Mod | Mods]),
+            dbg_out("Backend ~p initialized~n", [Backend])
+    end,
+    init_backends(Rest).
 
 init_backend(Mod, [_|_] = Aliases) ->
     case Mod:init_backend() of
@@ -177,6 +188,10 @@ init_backend(Mod, [_|_] = Aliases) ->
 	    mnesia:abort({backend_init_error, Error})
     end.
 
+get_backends_to_initialize(Ext) ->
+    lists:foldl(fun({Alias, Mod}, Acc) ->
+        orddict:append(Mod, Alias, Acc) end, orddict:new(), Ext).
+
 exit_on_error({error, Reason}) ->
     exit(Reason);
 exit_on_error(GoodRes) ->

lib/mnesia/test/Makefile

@@ -54,6 +54,7 @@ MODULES= \
 	mnesia_cost \
 	mnesia_dbn_meters \
 	ext_test \
+	ext_test_server \
 	mnesia_index_plugin_test \
 	mnesia_external_backend_test