Beam / Dataflow：未定义窗口的拓扑的maxTimestamp

Question

maxTimestamp对于全局窗口的预期行为是什么？ 我有一个带有无限来源的拓扑，该拓扑未指定窗口策略。当我访问BoundedWindow的maxTimestamp字段时，会得到一个将来的时间戳。这是预期的行为吗？

Answer 1

是的，这是预期的行为。全局窗口的末尾必须比Beam中可能的最大时间戳值小一些，在实践中通常称为+ infinity。

来自GlobalWindow.java的源代码：

 // Triggers use maxTimestamp to set timers' timestamp. Timers fires when
 // the watermark passes their timestamps. So, the maxTimestamp needs to be
 // smaller than the TIMESTAMP_MAX_VALUE.
 // One standard day is subtracted from TIMESTAMP_MAX_VALUE to make sure
 // the maxTimestamp is smaller than TIMESTAMP_MAX_VALUE even after rounding up
 // to seconds or minutes.
 private static final Instant END_OF_GLOBAL_WINDOW = extractMaxTimestampFromProto();