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From JoshRosen <...@git.apache.org>
Subject [GitHub] spark pull request #16989: [SPARK-19659] Fetch big blocks to disk when shuff...
Date Thu, 18 May 2017 07:20:50 GMT
Github user JoshRosen commented on a diff in the pull request:

    https://github.com/apache/spark/pull/16989#discussion_r117171649
  
    --- Diff: core/src/main/scala/org/apache/spark/internal/config/package.scala ---
    @@ -278,4 +278,21 @@ package object config {
             "spark.io.compression.codec.")
           .booleanConf
           .createWithDefault(false)
    +
    +  private[spark] val SHUFFLE_ACCURATE_BLOCK_THRESHOLD =
    +    ConfigBuilder("spark.shuffle.accurateBlkThreshold")
    +      .doc("When we compress the size of shuffle blocks in HighlyCompressedMapStatus,
we will " +
    +        "record the size accurately if it's above the threshold specified by this config.
This " +
    --- End diff --
    
    One edge-case to consider is the situation where every shuffle block is _just_ over this
threshold: in this case `HighlyCompressedMapStatus` won't really be doing any compression.
    
    Does it make sense to compare to the average and capture the sizes of blocks which are
more than some percent / threshold above the average? The number of such blocks will probably
be smaller and this might help to avoid worst-case behaviors or excessive bloating of the
map output status sizes were someone to set this configuration too low.


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