Question

UI在GCP Dataflow上具有python流传输管道，该管道从PubSub读取数千条消息，如下所示：

    with beam.Pipeline(options=pipeline_options) as p:
      lines = p | "read" >> ReadFromPubSub(topic=str(job_options.inputTopic))
      lines = lines | "decode" >> beam.Map(decode_message)
      lines = lines | "Parse" >> beam.Map(parse_json)
      lines = lines | beam.WindowInto(beam.window.FixedWindows(1*60))
      lines = lines | "Add device id key" >> beam.Map(lambda elem: (elem.get('id'), elem))
      lines = lines | "Group by key" >> beam.GroupByKey()
      lines = lines | "Abandon key" >> beam.Map(flatten)
      lines | "WriteToAvro" >> beam.io.WriteToAvro(job_options.outputLocation, schema=schema, file_name_suffix='.avro', mime_type='application/x-avro')

管道运行得很好，除非它从不产生任何输出。有什么想法吗？

Answer 1

您的代码似乎有一些问题。首先，关于null / None（您已修复）和ints / floats（在注释中注明）存在一些格式错误的数据。最后，WriteToAvro转换无法写入无界的PCollections。有一种解决方法，您可以定义一个新的sink并将其与WriteToFiles转换一起使用，该转换能够写入无界的PCollections。

请注意，在撰写本文时（2020-06-18），该方法不适用于Apache Beam Python SDK <= 2.23。这是因为Python选取器无法反序列化选取的Avro模式（请参见BEAM-6522）。在这种情况下，这迫使解决方案改为使用FastAvro。如果您手动升级莳萝，则可以使用Avro >> 0.3.1.1 和 Avro >> 1.9.0，但是请小心，因为目前尚未测试。

请注意，以下是解决方法：

from apache_beam.io.fileio import FileSink
from apache_beam.io.fileio import WriteToFiles
import fastavro

class AvroFileSink(FileSink):
    def __init__(self, schema, codec='deflate'):
        self._schema = schema
        self._codec = codec

    def open(self, fh):
        # This is called on every new bundle.
        self.writer = fastavro.write.Writer(fh, self._schema, self._codec)

    def write(self, record):
        # This is called on every element.
        self.writer.write(record)

    def flush(self):
        self.writer.flush()

此新接收器的用法如下：

import apache_beam as beam

# Replace the following with your schema.
schema = fastavro.schema.parse_schema({
    'name': 'row',
    'namespace': 'test',
    'type': 'record',
    'fields': [
        {'name': 'a', 'type': 'int'},
    ],
})

# Create the sink. This will be used by the WriteToFiles transform to write
# individual elements to the Avro file.
sink = AvroFileSink(schema=schema)

with beam.Pipeline(...) as p:
    lines = p | beam.ReadFromPubSub(...)
    lines = ...

    # This is where your new sink gets used. The WriteToFiles transform takes
    # the sink and uses it to write to a directory defined by the path 
    # argument.
    lines | WriteToFiles(path=job_options.outputLocation, sink=sink)

Beam Streaming管道不会将文件写入存储桶

1 个答案: