问题描述
我有一个从BigQuery获取数据并将其写入GCS的管道,但是,如果我发现任何拒绝,我都希望将它们纠正到Bigquery表中。我将拒绝收集到全局列表变量中,然后将列表加载到BigQuery表中。当我在本地运行它时,该过程可以正常工作,因为管道以正确的顺序运行。当我使用dataflowrunner运行它时,它不能保证顺序(我希望pipeline1在pipeline2之前运行。是否可以使用python在Dataflow中使用依赖的管道?或者也请建议是否可以使用更好的方法解决此问题。预先感谢。
with beam.Pipeline(options=PipelineOptions(pipeline_args)) as pipeline1:
data = (pipeline1
| 'get data' >> beam.io.Read(beam.io.BigQuerySource(query=...,use_standard_sql=True))
| 'combine output to list' >> beam.combiners.ToList()
| 'tranform' >> beam.Map(lambda x: somefunction) # Collecting rejects in the except block of this method to a global list variable
....etc
| 'to gcs' >> beam.io.WritetoText(output)
)
# Loading the rejects gathered in the above pipeline to Biquery
with beam.Pipeline(options=PipelineOptions(pipeline_args)) as pipeline2:
rejects = (pipeline2
| 'create pipeline' >> beam.Create(reject_list)
| 'to json format' >> beam.Map(lambda data: {.....})
| 'to bq' >> beam.io.WritetoBigQuery(....)
)
解决方法
您可以执行类似的操作,但只有1个管道,并且转换中需要一些其他代码。
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应该有两个输出:一个被写入GCS,一个被拒绝的元素最终将被写入BigQuery。
为此,您的转换函数将必须返回beam.Map(lambda x: somefunction)
。
Beam编程指南中有一个示例:https://beam.apache.org/documentation/programming-guide/#multiple-outputs-dofn
第二个TaggedOutput
,然后您可以写入BigQuery。
管道的第二个分支中不需要PCollection
。
管道将是这样的:
Create
然后with beam.Pipeline(options=PipelineOptions(pipeline_args)) as pipeline1:
data = (pipeline1
| 'get data' >> beam.io.Read(beam.io.BigQuerySource(query=...,use_standard_sql=True))
| 'combine output to list' >> beam.combiners.ToList()
| 'tranform' >> beam.Map(transform) # Tagged output produced here
pcoll_to_gcs = data.gcs_output
pcoll_to_bq = data.rejected
pcoll_to_gcs | "to gcs" >> beam.io.WriteToText(output)
pcoll_to_bq | "to bq" >> beam.io.WriteToBigQuery(....)
函数将是这样的
transform