使用 Python 在 Apache Beam 管道中进行异常处理

Question

我正在使用 python 中的 Apache Beam（在 GCP Dataflow 上）做一个简单的管道，从 PubSub 读取并在 Big Query 上写入，但无法处理管道上的异常以创建替代流。

在一个简单的 WriteToBigQuery 示例中：

output = json_output | 'Write to BigQuery' >> beam.io.WriteToBigQuery('some-project:dataset.table_name')

我试图把它放在一个try/except代码中，但它不起作用，因为当它失败时，异常似乎被抛出到我的 python 执行之外的 Java 层上：

INFO:root:2019-01-29T15:49:46.516Z: JOB_MESSAGE_ERROR: java.util.concurrent.ExecutionException: java.lang.RuntimeException: Error received from SDK harness for instruction -87: Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/apache_beam/runners/worker/sdk_worker.py", line 135, in _execute
    response = task()
  File "/usr/local/lib/python2.7/dist-packages/apache_beam/runners/worker/sdk_worker.py", line 170, in <lambda>
    self._execute(lambda: worker.do_instruction(work), work)
  File "/usr/local/lib/python2.7/dist-packages/apache_beam/runners/worker/sdk_worker.py", line 221, in do_instruction
    request.instruction_id)
...
...
...
    self.signature.finish_bundle_method.method_value())
  File "/usr/local/lib/python2.7/dist-packages/apache_beam/io/gcp/bigquery.py", line 1368, in finish_bundle
    self._flush_batch()
  File "/usr/local/lib/python2.7/dist-packages/apache_beam/io/gcp/bigquery.py", line 1380, in _flush_batch
    self.table_id, errors))
RuntimeError: Could not successfully insert rows to BigQuery table [<myproject:datasetname.tablename>]. Errors: [<InsertErrorsValueListEntry
 errors: [<ErrorProto
 debugInfo: u''
 location: u''
 message: u'Missing required field: object.teste.'
 reason: u'invalid'>]
 index: 0>] [while running 'generatedPtransform-63']

        java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:357)
        java.util.concurrent.CompletableFuture.get(CompletableFuture.java:1895)
        org.apache.beam.sdk.util.MoreFutures.get(MoreFutures.java:57)
        org.apache.beam.runners.dataflow.worker.fn.control.RegisterAndProcessBundleOperation.finish(RegisterAndProcessBundleOperation.java:276)
        org.apache.beam.runners.dataflow.worker.util.common.worker.MapTaskExecutor.execute(MapTaskExecutor.java:84)
        org.apache.beam.runners.dataflow.worker.fn.control.BeamFnMapTaskExecutor.execute(BeamFnMapTaskExecutor.java:119)
        org.apache.beam.runners.dataflow.worker.StreamingDataflowWorker.process(StreamingDataflowWorker.java:1228)
        org.apache.beam.runners.dataflow.worker.StreamingDataflowWorker.access$1000(StreamingDataflowWorker.java:143)
        org.apache.beam.runners.dataflow.worker.StreamingDataflowWorker$6.run(StreamingDataflowWorker.java:967)
        java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.RuntimeException: Error received from SDK harness for instruction -87: Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/apache_beam/runners/worker/sdk_worker.py", line 135, in _execute
    response = task()
  File "/usr/local/lib/python2.7/dist-packages/apache_beam/runners/worker/sdk_worker.py", line 170, in <lambda>
    self._execute(lambda: worker.do_instruction(work), work)
  File "/usr/local/lib/python2.7/dist-packages/apache_beam/runners/worker/sdk_worker.py", line 221, in do_instruction
    request.instruction_id)
  File "/usr/local/lib/python2.7/dist-packages/apache_beam/runners/worker/sdk_worker.py", line 237, in process_bundle
    bundle_processor.process_bundle(instruction_id)
...
...
...
    self.signature.finish_bundle_method.method_value())
  File "/usr/local/lib/python2.7/dist-packages/apache_beam/io/gcp/bigquery.py", line 1368, in finish_bundle
    self._flush_batch()
  File "/usr/local/lib/python2.7/dist-packages/apache_beam/io/gcp/bigquery.py", line 1380, in _flush_batch
    self.table_id, errors))

甚至试图处理这个：

RuntimeError: Could not successfully insert rows to BigQuery table [<myproject:datasetname.tablename>]. Errors: [<InsertErrorsValueListEntry
 errors: [<ErrorProto
 debugInfo: u''
 location: u''
 message: u'Missing required field: object.teste.'
 reason: u'invalid'>]
 index: 0>] [while running 'generatedPtransform-63']

使用：

try:
 ...
except RuntimeException as e:
 ...

或者使用泛型Exception不起作用。

我可以找到很多使用 Java 在 Apache Beam 中处理错误的例子，但在 python 处理错误中没有一个。

有谁知道如何得到这个？

Answer 1

我只能在DoFn级别上捕获异常，所以是这样的：

class MyPipelineStep(beam.DoFn):

    def process(self, element, *args, **kwargs):
        try:
            # do stuff...
            yield pvalue.TaggedOutput('main_output', output_element)
        except Exception as e:
            yield pvalue.TaggedOutput('exception', str(e))

然而WriteToBigQuery，PTransform它包裹了DoFn BigQueryWriteFn

所以你可能需要做这样的事情

class MyBigQueryWriteFn(BigQueryWriteFn):

    def process(self, *args, **kwargs):
        try:
            return super(BigQueryWriteFn, self).process(*args, **kwargs)
        except Exception as e:
            # Do something here

class MyWriteToBigQuery(WriteToBigQuery):
    # Copy the source code of `WriteToBigQuery` here, 
    # but replace `BigQueryWriteFn` with `MyBigQueryWriteFn`

https://beam.apache.org/releases/pydoc/2.9.0/_modules/apache_beam/io/gcp/bigquery.html#WriteToBigQuery