CODEWITHSUNDEEP
apache-flinkflink-streaming
jmhostalet
jmhostalet

Reputation: 4639

How to implement a LEFT OUTER JOIN with streams in Apache Flink

I have two streams left and right. For the same time window let's say that

I wonder how to implement a LEFT OUTER JOIN in Apache Flink so that the result obtained when processing this window is the following:

(L1, R1), (L2, null)

L1, R1 are matching by key (1), and L2, R3 do not match. L2 is included because is at left

Upvotes: 1

Views: 1625

Answers (1)

Dominik Wosiński
Dominik Wosiński

Reputation: 3864

Well, You should be able to obtain the proper results with the coGroup operator and properly implemented CoGroupFunction. The function gives You access to the whole group in the coGroup method. The documentation states that for CoGroupFunction one of the groups may be empty, so this should allow You to implement the Outer Join. The only issue is the fact that groups are currently created in memory, so You need to verify that Your groups won't grow too big as they can effectively kill the JVM.

Upvotes: 1

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