Apache Beam窗口:考虑较晚的数据，但仅发出一个窗格 [英] Apache beam windowing: consider late data but emit only one pane

问题描述

我想在水印到达窗口末尾x分钟后发出一个窗格.这让我确保可以处理一些较晚的数据，但仍只发出一个窗格.我目前正在使用Java.

I would like to emit a single pane when the watermark reaches x minutes past the end of the window. This let's me ensure I handle some late data, but still only emit one pane. I am currently working in java.

目前，我找不到适合该问题的解决方案.当水印到达窗口的末端时，我可以发出一个窗格，但是所有后期数据都将被丢弃.我可以在窗口末尾发出窗格，然后在收到较晚的数据时再次发出，但是在这种情况下，我不会发出单个窗格.

At the moment I can't find proper solutions to this problem. I could emit a single pane when the watermark reaches the end of the window, but then any late data is dropped. I could emit the pane at the end of the window and then again when I receive late data, however in this case I am not emitting a single pane.

我目前有与此类似的代码:

I currently have code similar to this:

.triggering(
    // This is going to emit the pane, but I don't want emit the pane yet!                                  
    AfterWatermark.pastEndOfWindow()

    // This is going to emit panes each time I receive late data, however 
    // I would like to only emit one pane at the end of the allowedLateness
).withAllowedLateness(allowedLateness).accumulatingFiredPanes())

万一仍然令人困惑，我只想在水印通过allowedLateness时只发出一个窗格.

In case there is still confusion, I would like to only emit a single pane when the watermark passes the allowedLateness.

推荐答案

感谢Guillem，最后我用您的答案找到了

Thanks Guillem, in the end I used your answer to find this very useful link with lots of apache beam examples. From this I came up with the following solution:

 // We first specify to never emit any panes
 .triggering(Never.ever())

 // We then specify to fire always when closing the window. This will emit a
 // single final pane at the end of allowedLateness
 .withAllowedLateness(allowedLateness, Window.ClosingBehavior.FIRE_ALWAYS)
 .discardingFiredPanes())

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