gzip - Flink 如何容错将数据作为 gzip 压缩下沉到 hdfs？

Question

我们想通过Flink的BucketingSink或者StreamingFileSink将压缩后的数据写入HDFS。我已经编写了自己的 Writer，如果没有发生故障，它可以正常工作。然而，当它遇到故障并从检查点重新启动时，它会生成有效长度的文件(hadoop < 2.7)或截断文件。不幸的是，gzip 是二进制文件，在文件末尾有尾部。因此，简单截断在我的情况下不起作用。为压缩 hdfs 接收器启用精确一次语义的任何想法？

这是我编写器的代码:

public class HdfsCompressStringWriter extends StreamWriterBaseV2<JSONObject> {

private static final long serialVersionUID = 2L;

/**
 * The {@code CompressFSDataOutputStream} for the current part file.
 */
private transient GZIPOutputStream compressionOutputStream;

public HdfsCompressStringWriter() {}

@Override
public void open(FileSystem fs, Path path) throws IOException {
    super.open(fs, path);
    this.setSyncOnFlush(true);
    compressionOutputStream = new GZIPOutputStream(this.getStream(), true);
}

public void close() throws IOException {
    if (compressionOutputStream != null) {
        compressionOutputStream.close();
        compressionOutputStream = null;
    }
    resetStream();
}

@Override
public void write(JSONObject element) throws IOException {
    if (element == null || !element.containsKey("body")) {
        return;
    }
    String content = element.getString("body") + "\n";
    compressionOutputStream.write(content.getBytes());
    compressionOutputStream.flush();
}

@Override
public Writer<JSONObject> duplicate() {
    return new HdfsCompressStringWriter();
}

Answer 1

我建议为 StreamingFileSink 实现一个 BulkWriter，它通过 GZIPOutputStream 压缩元素。代码可能如下所示:

public static void main(String[] args) throws Exception {
    StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
    env.setParallelism(1);
    env.enableCheckpointing(1000);

    final DataStream<Integer> input = env.addSource(new InfinitySource());

    final StreamingFileSink<Integer> streamingFileSink = StreamingFileSink.<Integer>forBulkFormat(new Path("output"), new GzipBulkWriterFactory<>()).build();
    input.addSink(streamingFileSink);

    env.execute();
}

private static class GzipBulkWriterFactory<T> implements BulkWriter.Factory<T> {
    @Override
    public BulkWriter<T> create(FSDataOutputStream fsDataOutputStream) throws IOException {
        final GZIPOutputStream gzipOutputStream = new GZIPOutputStream(fsDataOutputStream, true);
        return new GzipBulkWriter<>(new ObjectOutputStream(gzipOutputStream), gzipOutputStream);
    }
}

private static class GzipBulkWriter<T> implements BulkWriter<T> {

    private final GZIPOutputStream gzipOutputStream;
    private final ObjectOutputStream objectOutputStream;

    public GzipBulkWriter(ObjectOutputStream objectOutputStream, GZIPOutputStream gzipOutputStream) {
        this.gzipOutputStream = gzipOutputStream;
        this.objectOutputStream = objectOutputStream;
    }

    @Override
    public void addElement(T t) throws IOException {
        objectOutputStream.writeObject(t);
    }

    @Override
    public void flush() throws IOException {
        objectOutputStream.flush();
    }

    @Override
    public void finish() throws IOException {
        objectOutputStream.flush();
        gzipOutputStream.finish();
    }
}