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From "Lalwani, Jayesh" <Jayesh.Lalw...@capitalone.com>
Subject Re: Why doesn't spark use broadcast join?
Date Thu, 29 Mar 2018 14:54:54 GMT
Try putting a Broadcast hint like show here https://jaceklaskowski.gitbooks.io/mastering-spark-sql/spark-sql-hint-framework.html#sql-hints

From: Vitaliy Pisarev <vitaliy.pisarev@biocatch.com>
Date: Thursday, March 29, 2018 at 8:42 AM
To: "user@spark.apache.org" <user@spark.apache.org>
Subject: Why doesn't spark use broadcast join?

I am looking at the physical plan for the following query:


SELECT f1,f2,f3,...
FROM T1
LEFT ANTI JOIN T2 ON T1.id = T2.id
WHERE  f1 = 'bla'
       AND f2 = 'bla2'
       AND some_date >= date_sub(current_date(), 1)
LIMIT 100
An important detail: the table 'T1' can be very large (hundreds of thousands of rows), but
table T2 is rather small. Maximun in the thousands.
In this particular case, the table T2 has 2 rows.

In the physical plan, I see that a SortMergeJoin is performed. Despite it being the perfect
candidate for a broadcast join.

What could be the reason for this?
Is there a way to hint the optimizer to perform a broadcast join in the sql syntax?

I am writing this in pyspark and the query itself is over parquets stored in Azure blob storage.


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