Merge pull request #4027 from daipom/add-warning-for-restoring-buffer

buffer: warning message for restoring buffer with flush_at_shutdown

lib/fluent/plugin/buf_file.rb

@@ -145,7 +145,13 @@ def resume
         Dir.glob(escaped_patterns(patterns)) do |path|
           next unless File.file?(path)
 
-          log.debug { "restoring buffer file: path = #{path}" }
+          if owner.respond_to?(:buffer_config) && owner.buffer_config&.flush_at_shutdown
+            # When `flush_at_shutdown` is `true`, the remaining chunk files during resuming are possibly broken
+            # since there may be a power failure or similar failure.
+            log.warn { "restoring buffer file: path = #{path}" }
+          else
+            log.debug { "restoring buffer file: path = #{path}" }
+          end
 
           m = new_metadata() # this metadata will be overwritten by resuming .meta file content
                              # so it should not added into @metadata_list for now

lib/fluent/plugin/buf_file_single.rb

@@ -166,7 +166,13 @@ def resume
         Dir.glob(escaped_patterns(patterns)) do |path|
           next unless File.file?(path)
 
-          log.debug { "restoring buffer file: path = #{path}" }
+          if owner.respond_to?(:buffer_config) && owner.buffer_config&.flush_at_shutdown
+            # When `flush_at_shutdown` is `true`, the remaining chunk files during resuming are possibly broken
+            # since there may be a power failure or similar failure.
+            log.warn { "restoring buffer file: path = #{path}" }
+          else
+            log.debug { "restoring buffer file: path = #{path}" }
+          end
 
           m = new_metadata() # this metadata will be updated in FileSingleChunk.new
           mode = Fluent::Plugin::Buffer::FileSingleChunk.assume_chunk_state(path)