Re: streaming join implementation

Posted by Balaji Rajagopalan on
URL: http://deprecated-apache-flink-user-mailing-list-archive.369.s1.nabble.com/streaming-join-implementation-tp6095p6096.html

You can implement join in flink (which is a inner join) the below mentioned pseudo code . The below join is for a 5 minute interval, yes will be some corners cases when the data coming after 5 minutes will be  missed out in the join window, I actually had solved this problem but storing some data in redis and wrote correlation logic to take care of the corner cases that were missed out in the join  window. 

val output: DataStream[(OutputData)] = stream1.join(stream2).where(_.key1).equalTo(_.key2).
  window(TumblingEventTimeWindows.of(Time.of(5, TimeUnit.MINUTE))).apply(new SomeJoinFunction)

On Thu, Apr 14, 2016 at 10:02 AM, Henry Cai <[hidden email]> wrote:

Hi,

We are evaluating different streaming platforms.  For a typical join between two streams

select a.*, b.*

FROM a, b

ON a.id == b.id

How does flink implement the join?  The matching record from either stream can come late, we consider it's a valid join as long as the event time for record a and b are in the same day.

I think some streaming platform (e.g. google data flow) will store the records from both streams in a K/V lookup store and later do the lookup.  Is this how flink implement the streaming join?

If we need to store all the records in a state store, that's going to be a lots of records for a day.