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From Guy Doulberg <>
Subject FW: Big table join optimization
Date Fri, 31 Jan 2014 00:07:00 GMT

hi guys

I am trying to optimize a hive join query, I have a join of two big tables. The join between
them is taking too long, no matter how many reducers I set, there are always two reducers
struggling to finish  in the end of  the job
The job not always ends, sometime it fails with memory problems

In the fast completed reducers I can see:
7688459 rows: used memory = 991337736

In the long running reducers:

43363436 rows: used memory = 1142368456

At first I thought  am dealing with  skew key, but I set the   hive.optimize.skewjoin to true,
and  it didn't change a thing, I played with  hive.skewjoin.key also didn't change a thing

Any other ideas I can try?

I am using hive 0.10 of CDH4.2.1

the source tables are using customized   serdes

Guy Doulberg
Team leader @ Perion

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