Faster node start with many classic queues v2 (#7676)

* Faster all_queue_directory_names/1
* Optimise writing stub files

Combined, this reduces node startup time by half with many empty classic queues v2

2 files changed, 25 insertions, 8 deletions

diff --git a/deps/rabbit/src/rabbit_classic_queue_index_v2.erl b/deps/rabbit/src/rabbit_classic_queue_index_v2.erl
index d2e70324f3..51937558d7 100644
--- a/deps/rabbit/src/rabbit_classic_queue_index_v2.erl
+++ b/deps/rabbit/src/rabbit_classic_queue_index_v2.erl
@@ -205,8 +205,7 @@ init1(Name, Dir, OnSyncFun, OnSyncMsgFun) ->
 
 ensure_queue_name_stub_file(#resource{virtual_host = VHost, name = QName}, Dir) ->
     QueueNameFile = filename:join(Dir, ?QUEUE_NAME_STUB_FILE),
-    ok = filelib:ensure_dir(QueueNameFile),
-    ok = file:write_file(QueueNameFile, <<"VHOST: ", VHost/binary, "\n",
+    ok = write_file_and_ensure_dir(QueueNameFile, <<"VHOST: ", VHost/binary, "\n",
                                           "QUEUE: ", QName/binary, "\n",
                                           "INDEX: v2\n">>).
 
@@ -1292,3 +1291,14 @@ highest_continuous_seq_id([SeqId1, SeqId2|Tail], EndSeqId)
     highest_continuous_seq_id([SeqId2|Tail], EndSeqId);
 highest_continuous_seq_id([SeqId|Tail], _) ->
     {SeqId, Tail}.
+
+write_file_and_ensure_dir(Name, IOData) ->
+    case file:write_file(Name, IOData, [raw]) of
+        ok -> ok;
+        {error, enoent} ->
+            case filelib:ensure_dir(Name) of
+                ok -> file:write_file(Name, IOData, [raw]);
+                Err -> Err
+            end;
+         Err -> Err
+    end.
diff --git a/deps/rabbit/src/rabbit_queue_index.erl b/deps/rabbit/src/rabbit_queue_index.erl
index 34f956d674..37a05263fd 100644
--- a/deps/rabbit/src/rabbit_queue_index.erl
+++ b/deps/rabbit/src/rabbit_queue_index.erl
@@ -549,10 +549,12 @@ start(VHost, DurableQueueNames) ->
                    sets:add_element(DirName, ValidDirectories)}
           end, {[], sets:new()}, DurableQueueNames),
     %% Any queue directory we've not been asked to recover is considered garbage
-    _ = rabbit_file:recursive_delete(
-      [DirName ||
-        DirName <- all_queue_directory_names(VHost),
-        not sets:is_element(filename:basename(DirName), DurableDirectories)]),
+    ToDelete = [filename:join([rabbit_vhost:msg_store_dir_path(VHost), "queues", Dir])
+                || Dir <- lists:subtract(all_queue_directory_names(VHost),
+                                         sets:to_list(DurableDirectories))],
+    rabbit_log:debug("Deleting unknown files/folders: ~p", [ToDelete]),
+    _ = rabbit_file:recursive_delete(ToDelete),
+
     rabbit_recovery_terms:clear(VHost),
 
     %% The backing queue interface requires that the queue recovery terms
@@ -564,8 +566,13 @@ start(VHost, DurableQueueNames) ->
 stop(VHost) -> rabbit_recovery_terms:stop(VHost).
 
 all_queue_directory_names(VHost) ->
-    filelib:wildcard(filename:join([rabbit_vhost:msg_store_dir_path(VHost),
-                                    "queues", "*"])).
+    VHostQueuesPath = filename:join([rabbit_vhost:msg_store_dir_path(VHost), "queues"]),
+    case filelib:is_dir(VHostQueuesPath) of
+        true  ->
+                    {ok, Dirs} = file:list_dir(VHostQueuesPath),
+                    Dirs;
+        false -> []
+    end.
 
 %%----------------------------------------------------------------------------
 %% startup and shutdown