从BigQuery缓慢更改查找缓存-数据流Python流SDK

我试图遵循缓慢更改查找缓存的设计模式( https://cloud.google.com/blog/products/gcp/guide-to-common-cloud-dataflow-use-case-patterns-part-1 )对于使用Python SDK for Apache Beam on DataFlow的流管道。

查找缓存的引用表位于BigQuery中,我们可以读取它并将其作为ParDo操作的侧输入传入,但无论我们如何设置触发器/windows,它都不会刷新。

class FilterAlertDoFn(beam.DoFn):
  def process(self, element, alertlist):

    print len(alertlist)
    print alertlist

    …  # function logic

alert_input = (p | beam.io.Read(beam.io.BigQuerySource(query=ALERT_QUERY))
                        | ‘alert_side_input’ >> beam.WindowInto(
                            beam.window.GlobalWindows(),
                            trigger=trigger.RepeatedlyTrigger(trigger.AfterWatermark(
                                late=trigger.AfterCount(1)
                            )),
                            accumulation_mode=trigger.AccumulationMode.ACCUMULATING
                          )
                       | beam.Map(lambda elem: elem[‘SOMEKEY’])
)

...


main_input | ‘alerts’ >> beam.ParDo(FilterAlertDoFn(), beam.pvalue.AsList(alert_input))

基于此处的I/O页( https://beam.apache.org/documentation/io/built-in/ )它说Python SDK只支持BigQuery接收器的流,这是否意味着BQ读取是一个有界的源,因此不能在这个方法中刷新?

尝试在源上设置非全局窗口会导致侧输入中的PCollection为空。

更新 : 当尝试实现Pablo的答案所建议的策略时,使用side输入的ParDo操作不会运行。

有一个输入源指向两个输出,其中一个使用侧输入。非SideInput仍然会到达它的目的地,SideInput管道不会进入FilterAlertDoFn()。

通过将side输入替换为虚拟值,管道将进入该函数。也许是在等待一个不存在的合适窗口?

使用与上面相同的FilterAlertDoFn(),我的side_输入和调用现在看起来如下:

def refresh_side_input(_):
   query = 'select col from table'
   client = bigquery.Client(project='gcp-project')
   query_job = client.query(query)

   return query_job.result()


trigger_input = ( p | 'alert_ref_trigger' >> beam.io.ReadFromPubSub(
            subscription=known_args.trigger_subscription))


bigquery_side_input = beam.pvalue.AsSingleton((trigger_input
         | beam.WindowInto(beam.window.GlobalWindows(),
                           trigger=trigger.Repeatedly(trigger.AfterCount(1)),
                           accumulation_mode=trigger.AccumulationMode.DISCARDING)
         | beam.Map(refresh_side_input)
        ))

...

# Passing this as side input doesn't work
main_input | 'alerts' >> beam.ParDo(FilterAlertDoFn(), bigquery_side_input)

# Passing dummy variable as side input does work
main_input | 'alerts' >> beam.ParDo(FilterAlertDoFn(), [1])

我尝试了几个不同版本的refresh_side_input(),它们在检查函数内部的返回时报告预期结果。

更新2:

我对Pablo的代码做了一些小修改,得到了相同的行为——DoFn永远不会执行。

在下面的示例中,每当我发布到 一些其他的话题 但在发布到时将永远看不到“in-DoFn” 一些话题

import apache_beam as beam
import apache_beam.transforms.window as window

from apache_beam.transforms import trigger
from apache_beam.options.pipeline_options import PipelineOptions
from apache_beam.options.pipeline_options import SetupOptions
from apache_beam.options.pipeline_options import StandardOptions


def load_my_conversion_data():
    return {'EURUSD': 1.1, 'USDMXN': 4.4}


def load_conversion_data(_):
    # I will suppose that these are currency conversions. E.g.
    # {'EURUSD': 1.1, 'USDMXN' 20,}
    print 'in_load_conversion_data'
    return load_my_conversion_data()


class ConvertTo(beam.DoFn):
    def __init__(self, target_currency):
        self.target_currency = target_currency

    def process(self, elm, rates):
        print 'in_DoFn'
        elm = elm.attributes
        if elm['currency'] == self.target_currency:
            yield elm
        elif ' % s % s' % (elm['currency'], self.target_currency) in rates:
            rate = rates[' % s % s' % (elm['currency'], self.target_currency)]
            result = {}.update(elm).update({'currency': self.target_currency,
            'value': elm['value']*rate})
             yield result
         else:
             return  # We drop that value


pipeline_options = PipelineOptions()
pipeline_options.view_as(StandardOptions).streaming = True
p = beam.Pipeline(options=pipeline_options)

some_topic = 'projects/some_project/topics/some_topic'
some_other_topic = 'projects/some_project/topics/some_other_topic'

with beam.Pipeline(options=pipeline_options) as p:

    table_pcv = beam.pvalue.AsSingleton((
      p
      | 'some_other_topic' >>  beam.io.ReadFromPubSub(topic=some_other_topic,  with_attributes=True)
      | 'some_other_window' >> beam.WindowInto(window.GlobalWindows(),
                        trigger=trigger.Repeatedly(trigger.AfterCount(1)),
                        accumulation_mode=trigger.AccumulationMode.DISCARDING)
      | beam.Map(load_conversion_data)))


    _ = (p | 'some_topic' >> beam.io.ReadFromPubSub(topic=some_topic)
         | 'some_window' >> beam.WindowInto(window.FixedWindows(1))
         | beam.ParDo(ConvertTo('USD'), rates=table_pcv))