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From YuhuWang2002 <>
Subject [GitHub] spark issue #15297: [SPARK-9862]Handling data skew
Date Tue, 25 Oct 2016 06:10:06 GMT
Github user YuhuWang2002 commented on the issue:
    I do some performance test between use skew join algorithm and not use skew join  algorithm.
    I generate 2 table with 1/5 data skew in table S and 1/10000 data skew in table R. Two
table skew in same key.
    spark.sql.adaptive.skewjoin.threshold   6000000
    spark.sql.adaptive.shuffle.targetPostShuffleInputSize   5000000
    record: S 10000000 rows; R 100000000 rows
    select count(*) from R,S where rid=sid and sname>'wang9' and rname > 'zhang9';
    skew algorithm : 167.695s
    normal algorithm: 303.922s
    R2_txt is 100000000 rows without data skew.
    sql: select count(*) from R2_txt,S where rid=sid and sname>'wang' and rname > 'zhang9';
    skew algorithm : 38.717s
    normal algorithm: 114.21s

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