Don't scan for valid messages when deleting

Looking for valid messages before deleting a message store file
was an old check for extra safety. However, it is a bottleneck
under intense workload: it can take a few seconds to delete a file
(a vast majority of that spent scanning for messages), while new
files can be created faster than that. That leads to the disk usage
growing, even if the number of messages in the queues is not.

We are not aware of any situations where this check actually found
valid messages in a file that was requested to be deleted.
This is a well tested code path a this point, so let's just remove
the extra check.

Author: mkuratczyk

deps/rabbit/src/rabbit_msg_store.erl

@@ -2123,9 +2123,9 @@ truncate_file(File, Size, ThresholdTimestamp, #gc_state{ file_summary_ets = File
 
 -spec delete_file(non_neg_integer(), gc_state()) -> ok | defer.
 
-delete_file(File, State = #gc_state { file_summary_ets = FileSummaryEts,
-                                      file_handles_ets = FileHandlesEts,
-                                      dir              = Dir }) ->
+delete_file(File, #gc_state { file_summary_ets = FileSummaryEts,
+                              file_handles_ets = FileHandlesEts,
+                              dir              = Dir }) ->
     case ets:match_object(FileHandlesEts, {{'_', File}, '_'}, 1) of
         {[_|_], _Cont} ->
             rabbit_log:debug("Asked to delete file ~p but it has active readers. Deferring.",
@@ -2134,7 +2134,6 @@ delete_file(File, State = #gc_state { file_summary_ets = FileSummaryEts,
         _ ->
             [#file_summary{ valid_total_size = 0,
                             file_size = FileSize }] = ets:lookup(FileSummaryEts, File),
-            [] = scan_and_vacuum_message_file(File, State),
             ok = file:delete(form_filename(Dir, filenum_to_name(File))),
             true = ets:delete(FileSummaryEts, File),
             rabbit_log:debug("Deleted empty file number ~tp; reclaimed ~tp bytes", [File, FileSize]),