[GitHub] spark pull request: [SPARK-2236][SQL]SparkSQL add SkewJoin

[YanjieGao]

Github user YanjieGao commented on the pull request:

    https://github.com/apache/spark/pull/1134#issuecomment-48707013
  
    Thanks Michael ,
    (1) We could make it as a user hint ,like hive does .
    set hive.optimize.skewjoin = true; 
    set hive.skewjoin.key = skew_key_threshold （default = 100000）
    We could use  set sparksql.optimize.skewjoin=true
                            set sparksql.skewjoin.key=skew_key_threshold
    (2)We could use sample to found the relative num of the key and though 
skew_key_threshold which is user set can judge which key is over the threshold
    (3) toString will generate many singleton object .
    ,I will optimize the code in next step.



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