chore(ds): slightly simplify working with storage generations

apps/emqx_durable_storage/src/emqx_ds_storage_layer.erl

@@ -259,14 +259,14 @@ get_streams(Shard, TopicFilter, StartTime) ->
     lists:flatmap(
         fun(GenId) ->
             ?tp(get_streams_get_gen, #{gen_id => GenId}),
-            case generation_get_safe(Shard, GenId) of
-                {ok, #{module := Mod, data := GenData}} ->
+            case generation_get(Shard, GenId) of
+                #{module := Mod, data := GenData} ->
                     Streams = Mod:get_streams(Shard, GenData, TopicFilter, StartTime),
                     [
                         {GenId, ?stream_v2(GenId, InnerStream)}
                      || InnerStream <- Streams
                     ];
-                {error, not_found} ->
+                not_found ->
                     %% race condition: generation was dropped before getting its streams?
                     []
             end
@@ -282,14 +282,14 @@ get_delete_streams(Shard, TopicFilter, StartTime) ->
     lists:flatmap(
         fun(GenId) ->
             ?tp(get_streams_get_gen, #{gen_id => GenId}),
-            case generation_get_safe(Shard, GenId) of
-                {ok, #{module := Mod, data := GenData}} ->
+            case generation_get(Shard, GenId) of
+                #{module := Mod, data := GenData} ->
                     Streams = Mod:get_delete_streams(Shard, GenData, TopicFilter, StartTime),
                     [
                         ?delete_stream(GenId, InnerStream)
                      || InnerStream <- Streams
                     ];
-                {error, not_found} ->
+                not_found ->
                     %% race condition: generation was dropped before getting its streams?
                     []
             end
@@ -302,8 +302,8 @@ get_delete_streams(Shard, TopicFilter, StartTime) ->
 make_iterator(
     Shard, ?stream_v2(GenId, Stream), TopicFilter, StartTime
 ) ->
-    case generation_get_safe(Shard, GenId) of
-        {ok, #{module := Mod, data := GenData}} ->
+    case generation_get(Shard, GenId) of
+        #{module := Mod, data := GenData} ->
             case Mod:make_iterator(Shard, GenData, Stream, TopicFilter, StartTime) of
                 {ok, Iter} ->
                     {ok, #{
@@ -314,7 +314,7 @@ make_iterator(
                 {error, _} = Err ->
                     Err
             end;
-        {error, not_found} ->
+        not_found ->
             {error, unrecoverable, generation_not_found}
     end.
 
@@ -323,8 +323,8 @@ make_iterator(
 make_delete_iterator(
     Shard, ?delete_stream(GenId, Stream), TopicFilter, StartTime
 ) ->
-    case generation_get_safe(Shard, GenId) of
-        {ok, #{module := Mod, data := GenData}} ->
+    case generation_get(Shard, GenId) of
+        #{module := Mod, data := GenData} ->
             case Mod:make_delete_iterator(Shard, GenData, Stream, TopicFilter, StartTime) of
                 {ok, Iter} ->
                     {ok, #{
@@ -335,7 +335,7 @@ make_delete_iterator(
                 {error, _} = Err ->
                     Err
             end;
-        {error, not_found} ->
+        not_found ->
             {error, end_of_stream}
     end.
 
@@ -346,8 +346,8 @@ update_iterator(
     #{?tag := ?IT, ?generation := GenId, ?enc := OldIter},
     DSKey
 ) ->
-    case generation_get_safe(Shard, GenId) of
-        {ok, #{module := Mod, data := GenData}} ->
+    case generation_get(Shard, GenId) of
+        #{module := Mod, data := GenData} ->
             case Mod:update_iterator(Shard, GenData, OldIter, DSKey) of
                 {ok, Iter} ->
                     {ok, #{
@@ -358,15 +358,15 @@ update_iterator(
                 {error, _} = Err ->
                     Err
             end;
-        {error, not_found} ->
+        not_found ->
             {error, unrecoverable, generation_not_found}
     end.
 
 -spec next(shard_id(), iterator(), pos_integer()) ->
     emqx_ds:next_result(iterator()).
 next(Shard, Iter = #{?tag := ?IT, ?generation := GenId, ?enc := GenIter0}, BatchSize) ->
-    case generation_get_safe(Shard, GenId) of
-        {ok, #{module := Mod, data := GenData}} ->
+    case generation_get(Shard, GenId) of
+        #{module := Mod, data := GenData} ->
             Current = generation_current(Shard),
             case Mod:next(Shard, GenData, GenIter0, BatchSize) of
                 {ok, _GenIter, []} when GenId < Current ->
@@ -379,7 +379,7 @@ next(Shard, Iter = #{?tag := ?IT, ?generation := GenId, ?enc := GenIter0}, Batch
                 Error = {error, _, _} ->
                     Error
             end;
-        {error, not_found} ->
+        not_found ->
             %% generation was possibly dropped by GC
             {error, unrecoverable, generation_not_found}
     end.
@@ -392,8 +392,8 @@ delete_next(
     Selector,
     BatchSize
 ) ->
-    case generation_get_safe(Shard, GenId) of
-        {ok, #{module := Mod, data := GenData}} ->
+    case generation_get(Shard, GenId) of
+        #{module := Mod, data := GenData} ->
             Current = generation_current(Shard),
             case Mod:delete_next(Shard, GenData, GenIter0, Selector, BatchSize) of
                 {ok, _GenIter, _Deleted = 0, _IteratedOver = 0} when GenId < Current ->
@@ -406,7 +406,7 @@ delete_next(
                 Error = {error, _} ->
                     Error
             end;
-        {error, not_found} ->
+        not_found ->
             %% generation was possibly dropped by GC
             {ok, end_of_stream}
     end.
@@ -777,18 +777,13 @@ generation_current(Shard) ->
     #{current_generation := Current} = get_schema_runtime(Shard),
     Current.
 
--spec generation_get(shard_id(), gen_id()) -> generation().
+-spec generation_get(shard_id(), gen_id()) -> generation() | not_found.
 generation_get(Shard, GenId) ->
-    {ok, GenData} = generation_get_safe(Shard, GenId),
-    GenData.
-
--spec generation_get_safe(shard_id(), gen_id()) -> {ok, generation()} | {error, not_found}.
-generation_get_safe(Shard, GenId) ->
     case get_schema_runtime(Shard) of
         #{?GEN_KEY(GenId) := GenData} ->
-            {ok, GenData};
+            GenData;
         #{} ->
-            {error, not_found}
+            not_found
     end.
 
 -spec generations_since(shard_id(), emqx_ds:time()) -> [gen_id()].