Event time and process time in the flink

• Window
• Sliding time window
• Can be overlapping
• timeWindowAll(Time size, Time slide)
• Tumbling time window
• No overlapping
• timeWindowAll(Time size)
• Event Time based system
  env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime)
• Process Time base system
  env.setStreamTimeCharacteristic(TimeCharacteristic.ProcessingTime)
  
  
•  Watermark
• Work for event time.
• Define when to stop waiting for the events.
• Events are in order, then watermarks are just periodic markers in the stream.
• In out of order stream, define all events up to certain timestamp should have arrived.
  
  w(17) : point of timestamp if incoming elements smaller than 17, then ignore them.
  w(11) : point of timestamp if incoming elements smaller than 11, then ignore them.
  
  
•  Late Events
• Event arrived after watermark timestamp.
• Dropped by the default.
• Allowed lateness. Keep window state, until expired.

See more detail.