Fix a bug that BufferChunkOverflowError cause a whole data loss

lib/fluent/plugin/buffer.rb

@@ -332,12 +332,14 @@ def write(metadata_and_data, format: nil, size: nil, enqueue: false)
         unstaged_chunks = {} # metadata => [chunk, chunk, ...]
         chunks_to_enqueue = []
         staged_bytesizes_by_chunk = {}
+        # track internal BufferChunkOverflowError in write_step_by_step
+        buffer_chunk_overflow_errors = []
 
         begin
           # sort metadata to get lock of chunks in same order with other threads
           metadata_and_data.keys.sort.each do |metadata|
             data = metadata_and_data[metadata]
-            write_once(metadata, data, format: format, size: size) do |chunk, adding_bytesize|
+            write_once(metadata, data, format: format, size: size) do |chunk, adding_bytesize, error|
               chunk.mon_enter # add lock to prevent to be committed/rollbacked from other threads
               operated_chunks << chunk
               if chunk.staged?
@@ -352,6 +354,9 @@ def write(metadata_and_data, format: nil, size: nil, enqueue: false)
                 unstaged_chunks[metadata] ||= []
                 unstaged_chunks[metadata] << chunk
               end
+              if error && !error.empty?
+                buffer_chunk_overflow_errors << error
+              end
             end
           end
 
@@ -444,6 +449,10 @@ def write(metadata_and_data, format: nil, size: nil, enqueue: false)
             end
             chunk.mon_exit rescue nil # this may raise ThreadError for chunks already committed
           end
+          unless buffer_chunk_overflow_errors.empty?
+            # Notify delayed BufferChunkOverflowError here
+            raise BufferChunkOverflowError, buffer_chunk_overflow_errors.join(", ")
+          end
         end
       end
 
@@ -716,6 +725,7 @@ def write_once(metadata, data, format: nil, size: nil, &block)
 
       def write_step_by_step(metadata, data, format, splits_count, &block)
         splits = []
+        errors = []
         if splits_count > data.size
           splits_count = data.size
         end
@@ -761,18 +771,41 @@ def write_step_by_step(metadata, data, format, splits_count, &block)
             begin
               while writing_splits_index < splits.size
                 split = splits[writing_splits_index]
+                formatted_split = format ? format.call(split) : split.first
+                if split.size == 1 && original_bytesize == 0
+                  if format == nil && @compress != :text
+                    # The actual size of chunk is not determined until after chunk.append.
+                    # so, keep already processed 'split' content here.
+                    # (allow performance regression a bit)
+                    chunk.commit
+                  else
+                    big_record_size = formatted_split.bytesize
+                    if chunk.bytesize + big_record_size > @chunk_limit_size
+                      errors << "a #{big_record_size} bytes record (nth: #{writing_splits_index}) is larger than buffer chunk limit size"
+                      writing_splits_index += 1
+                      next
+                    end
+                  end
+                end
+
                 if format
-                  chunk.concat(format.call(split), split.size)
+                  chunk.concat(formatted_split, split.size)
                 else
                   chunk.append(split, compress: @compress)
                 end
 
                 if chunk_size_over?(chunk) # split size is larger than difference between size_full? and size_over?
+                  adding_bytes = chunk.instance_eval { @adding_bytes } || "N/A" # 3rd party might not have 'adding_bytes'
                   chunk.rollback
 
                   if split.size == 1 && original_bytesize == 0
-                    big_record_size = format ? format.call(split).bytesize : split.first.bytesize
-                    raise BufferChunkOverflowError, "a #{big_record_size}bytes record is larger than buffer chunk limit size"
+                    # It is obviously case that BufferChunkOverflowError should be raised here,
+                    # but if it raises here, already processed 'split' or
+                    # the proceeding 'split' will be lost completely.
+                    # so it is a last resort to delay raising such a exception
+                    errors << "a #{adding_bytes} bytes record (nth: #{writing_splits_index}) is larger than buffer chunk limit size"
+                    writing_splits_index += 1
+                    next
                   end
 
                   if chunk_size_full?(chunk) || split.size == 1
@@ -795,7 +828,8 @@ def write_step_by_step(metadata, data, format, splits_count, &block)
               raise
             end
 
-            block.call(chunk, chunk.bytesize - original_bytesize)
+            block.call(chunk, chunk.bytesize - original_bytesize, errors)
+            errors = []
           end
         end
       rescue ShouldRetry

test/plugin/test_buffer.rb

@@ -18,7 +18,7 @@ class DummyOutputPlugin < Fluent::Plugin::Base
   end
   class DummyMemoryChunkError < StandardError; end
   class DummyMemoryChunk < Fluent::Plugin::Buffer::MemoryChunk
-    attr_reader :append_count, :rollbacked, :closed, :purged
+    attr_reader :append_count, :rollbacked, :closed, :purged, :chunk
     attr_accessor :failing
     def initialize(metadata, compress: :text)
       super
@@ -944,6 +944,52 @@ def create_chunk_es(metadata, es)
         @p.write({@dm0 => es}, format: @format)
       end
     end
+
+    data(
+      first_chunk: Fluent::ArrayEventStream.new([[event_time('2016-04-11 16:00:02 +0000'), {"message" => "x" * 1_280_000}],
+                                                 [event_time('2016-04-11 16:00:02 +0000'), {"message" => "a"}],
+                                                 [event_time('2016-04-11 16:00:02 +0000'), {"message" => "b"}]]),
+      intermediate_chunk: Fluent::ArrayEventStream.new([[event_time('2016-04-11 16:00:02 +0000'), {"message" => "a"}],
+                                                        [event_time('2016-04-11 16:00:02 +0000'), {"message" => "x" * 1_280_000}],
+                                                        [event_time('2016-04-11 16:00:02 +0000'), {"message" => "b"}]]),
+      last_chunk: Fluent::ArrayEventStream.new([[event_time('2016-04-11 16:00:02 +0000'), {"message" => "a"}],
+                                                [event_time('2016-04-11 16:00:02 +0000'), {"message" => "b"}],
+                                                [event_time('2016-04-11 16:00:02 +0000'), {"message" => "x" * 1_280_000}]]),
+      multiple_chunks: Fluent::ArrayEventStream.new([[event_time('2016-04-11 16:00:02 +0000'), {"message" => "a"}],
+                                                     [event_time('2016-04-11 16:00:02 +0000'), {"message" => "x" * 1_280_000}],
+                                                     [event_time('2016-04-11 16:00:02 +0000'), {"message" => "b"}],
+                                                     [event_time('2016-04-11 16:00:02 +0000'), {"message" => "x" * 1_280_000}]])
+    )
+    test '#write exceeds chunk_limit_size, raise BufferChunkOverflowError, but not lost whole messages' do |(es)|
+      assert_equal [@dm0], @p.stage.keys
+      assert_equal [], @p.queue.map(&:metadata)
+
+      assert_equal 1_280_000, @p.chunk_limit_size
+
+      nth = []
+      es.entries.each_with_index do |entry, index|
+        if entry.last["message"].size == @p.chunk_limit_size
+          nth << index
+        end
+      end
+      messages = []
+      nth.each do |n|
+        messages << "a 1280025 bytes record (nth: #{n}) is larger than buffer chunk limit size"
+      end
+
+      assert_raise Fluent::Plugin::Buffer::BufferChunkOverflowError.new(messages.join(", ")) do
+        @p.write({@dm0 => es}, format: @format)
+      end
+      # message a and b are concatenated and staged
+      staged_messages = Fluent::MessagePackFactory.msgpack_unpacker.feed_each(@p.stage[@dm0].chunk).collect do |record|
+        record.last
+      end
+      assert_equal([2, [{"message" => "a"}, {"message" => "b"}]],
+                   [@p.stage[@dm0].size, staged_messages])
+      # only es0 message is queued
+      assert_equal [@dm0], @p.queue.map(&:metadata)
+      assert_equal [5000], @p.queue.map(&:size)
+    end
   end
 
   sub_test_case 'custom format with configuration for test with lower chunk limit size' do
@@ -1201,6 +1247,7 @@ def create_chunk_es(metadata, es)
   sub_test_case 'when compress is gzip' do
     setup do
       @p = create_buffer({'compress' => 'gzip'})
+      @dm0 = create_metadata(Time.parse('2016-04-11 16:00:00 +0000').to_i, nil, nil)
     end
 
     test '#compress returns :gzip' do
@@ -1211,6 +1258,30 @@ def create_chunk_es(metadata, es)
       chunk = @p.generate_chunk(create_metadata)
       assert chunk.singleton_class.ancestors.include?(Fluent::Plugin::Buffer::Chunk::Decompressable)
     end
+
+    test '#write compressed data which exceeds chunk_limit_size, it raises BufferChunkOverflowError' do
+      @p = create_buffer({'compress' => 'gzip', 'chunk_limit_size' => 70})
+      timestamp = event_time('2016-04-11 16:00:02 +0000')
+      es = Fluent::ArrayEventStream.new([[timestamp, {"message" => "012345"}], # overflow
+                                         [timestamp, {"message" => "aaa"}],
+                                         [timestamp, {"message" => "bbb"}]])
+      assert_equal [], @p.queue.map(&:metadata)
+      assert_equal 70, @p.chunk_limit_size
+
+      # calculate the actual boundary value. it varies on machine
+      c = @p.generate_chunk(create_metadata)
+      c.append(Fluent::ArrayEventStream.new([[timestamp, {"message" => "012345"}]]), compress: :gzip)
+      overflow_bytes = c.bytesize
+
+      messages = "a #{overflow_bytes} bytes record (nth: 0) is larger than buffer chunk limit size"
+      assert_raise Fluent::Plugin::Buffer::BufferChunkOverflowError.new(messages) do
+        # test format == nil && compress == :gzip
+        @p.write({@dm0 => es})
+      end
+      # message a and b occupies each chunks in full, so both of messages are queued (no staged chunk)
+      assert_equal([2, [@dm0, @dm0], [1, 1], nil],
+                   [@p.queue.size, @p.queue.map(&:metadata), @p.queue.map(&:size), @p.stage[@dm0]])
+    end
   end
 
   sub_test_case '#statistics' do