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From: jinfengni <git@git.apache.org>
To: dev@drill.apache.org
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References: <git-pr-704-drill@git.apache.org>
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Subject: [GitHub] drill pull request #704: DRILL-5125: Provide option to use generic code for ...
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Message-Id: <20170330231244.97E57E024D@git1-us-west.apache.org>
Date: Thu, 30 Mar 2017 23:12:44 +0000 (UTC)
archived-at: Thu, 30 Mar 2017 23:12:47 -0000

Github user jinfengni commented on a diff in the pull request:

    https://github.com/apache/drill/pull/704#discussion_r109058076
  
    --- Diff: exec/vector/src/main/codegen/templates/FixedValueVectors.java ---
    @@ -281,6 +282,11 @@ public void copyFromSafe(int fromIndex, int thisIndex, ${minor.class}Vector from
         copyFrom(fromIndex, thisIndex, from);
       }
     
    +  @Override
    +  public void copyEntry(int toIndex, ValueVector from, int fromIndex) {
    +    ((${minor.class}Vector) from).data.getBytes(fromIndex * ${type.width}, data, toIndex * ${type.width}, ${type.width});
    --- End diff --
    
    Throughout all the value vector classes, this new "copyEntry" method has to explicitly downcast from interface ValueVector to a subclass. Such cast happens for each value copied. I' not sure how performance overhead it could possibly incur : JVM has to check the input type, and raise ClassCastException in case of error. 
    
    Compared with the existing method,  I think cast only happens in doSetup(), which is called for each new schema. 
    
    Also, "copyEntry" uses data.getBytes(), while copyFromSafe() uses setInt(...,   from.data.getInt()).  I'm not sure the performance difference comes from the difference of generated code vs generic class, or the difference of the underneath implementation.
    
     
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