Join happening after watermark time

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Join happening after watermark time

Abhijeet Kumar
Hello Team,

I’m using watermark to join two streams as you can see below:

val order_wm = order_details.withWatermark("tstamp_trans", "20 seconds")
val invoice_wm = invoice_details.withWatermark("tstamp_trans", "20 seconds")
val join_df = order_wm
.join(invoice_wm, order_wm.col("s_order_id") === invoice_wm.col("order_id"))

My understanding with the above code, it will keep each of the stream for 20 secs. After it comes but, when I’m giving one stream now and the another after 20secs then also both are getting joined. It seems like even after watermark got finished it’s holding the data in memory. I tried even after 45 seconds and that was getting joined too.

This is creating confusion in my mind regarding watermark.

Thank you,
Abhijeet Kumar