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hadoopapache-sparkapache-pigbigdata
ihadanny
ihadanny

Reputation: 4483

In spark join, does table order matter like in pig?

Related to Spark - Joining 2 PairRDD elements

When doing a regular join in pig, the last table in the join is not brought into memory but streamed through instead, so if A has small cardinality per key and B large cardinality, it is significantly better to do join A, B than join A by B, from performance perspective (avoiding spill and OOM)

Is there a similar concept in spark? I didn't see any such recommendation, and wonder how is it possible? The implementation looks to me pretty much the same as in pig: https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/rdd/CoGroupedRDD.scala

Or am I missing something?

Upvotes: 12

Views: 3362

Answers (1)

aaronman
aaronman

Reputation: 18751

It does not make a difference, in spark the RDD will only be brought into memory if it is cached. So in spark to achieve the same effect you can cache the smaller RDD. Another thing you can do in spark which I'm not sure that pig does, is if all RDD's being joined have the same partitioner no shuffle needs to be done.

Upvotes: 6

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