Prioritise delete calls

Without this change, if the compaction was lagging behind,
we could have file deletion requests queued behind compaction
requests, leading to many unnecessary compactions.

Author: mkuratczyk

deps/rabbit/src/rabbit_msg_store.erl

@@ -1998,10 +1998,21 @@ delete_file_if_empty(File, State = #msstate {
 %% We do not try to look at messages that are not the last because we do not want to
 %% accidentally write over messages that were moved earlier.
 
-compact_file(File, State = #gc_state { index_ets        = IndexEts,
-                                       file_summary_ets = FileSummaryEts,
-                                       dir              = Dir,
-                                       msg_store        = Server }) ->
+compact_file(File, State = #gc_state { file_summary_ets = FileSummaryEts }) ->
+    case ets:lookup(FileSummaryEts, File) of
+        [] ->
+            rabbit_log:debug("File ~tp has already been deleted; no need to compact",
+                             [File]),
+            ok;
+        [#file_summary{file_size = FileSize}] ->
+            compact_file(File, FileSize, State)
+    end.
+
+compact_file(File, FileSize,
+             State = #gc_state { index_ets        = IndexEts,
+                                 file_summary_ets = FileSummaryEts,
+                                 dir              = Dir,
+                                 msg_store        = Server }) ->
     %% Get metadata about the file. Will be used to calculate
     %% how much data was reclaimed as a result of compaction.
     [#file_summary{file_size = FileSize}] = ets:lookup(FileSummaryEts, File),

deps/rabbit/src/rabbit_msg_store_gc.erl

@@ -12,7 +12,7 @@
 -export([start_link/1, compact/2, truncate/4, delete/2, stop/1]).
 
 -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
-         terminate/2, code_change/3]).
+         terminate/2, code_change/3, prioritise_cast/3]).
 
 -record(state,
         { pending,
@@ -51,6 +51,9 @@ delete(Server, File) ->
 stop(Server) ->
     gen_server2:call(Server, stop, infinity).
 
+prioritise_cast({delete, _}, _Len, _State) -> 5;
+prioritise_cast(_, _Len, _State) -> 0.
+
 %%----------------------------------------------------------------------------
 
 init([MsgStoreState]) ->