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From "Saumitra Shahapure (Vizury)" <saumitra.shahap...@vizury.com>
Subject Re: Spark performance for small queries
Date Thu, 22 Jan 2015 11:03:39 GMT
Hello,

We were comparing performance of some of our production hive queries
between Hive and Spark. We compared Hive(0.13)+hadoop (1.2.1) against both
Spark 0.9 and 1.1. We could see that the performance gains have been good
in Spark.

We tried a very simple query,
select count(*) from T where col3=123
in both sparkSQL and Hive (with hive.map.aggr=true) and found that Spark
performance had been 2x better than Hive (120sec vs 60sec). Table T is
stored in S3 and contains 600MB single GZIP file.

My question is, why Spark is faster than Hive here? In both of the cases,
the file will be downloaded, uncompressed and lines will be counted by a
single process. For Hive case, reducer will be identity function
since hive.map.aggr is true.

Note that disk spills and network I/O are very less for Hive's case as well,

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