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From paul-rogers <...@git.apache.org>
Subject [GitHub] drill pull request #901: DRILL-5709: Provide a value vector method to conver...
Date Sat, 12 Aug 2017 19:12:19 GMT
Github user paul-rogers commented on a diff in the pull request:

    https://github.com/apache/drill/pull/901#discussion_r132824832
  
    --- Diff: exec/vector/src/main/java/org/apache/drill/exec/vector/BaseValueVector.java
---
    @@ -133,5 +134,21 @@ public static boolean checkBufRefs(final ValueVector vv) {
       public BufferAllocator getAllocator() {
         return allocator;
       }
    +
    +  public static void fillBitsVector(UInt1Vector bits, int valueCount) {
    +
    +    // Create a new bits vector, all values non-null
    +
    +    bits.allocateNew(valueCount);
    +    UInt1Vector.Mutator bitsMutator = bits.getMutator();
    +    for (int i = 0; i < valueCount; i++) {
    +      bitsMutator.set(i, 1);
    +    }
    --- End diff --
    
    Sadly, Netty's `PlatformDependent` provides no equivalent of `memset`. Some tricks we
could do, if tests show we have a performance issue:
    
    * Use `setLong()` to write the value 0x01010101010101L every 8 values, with bytes for
the last < 8 values.
    * Create a heap buffer of some length n, filled with 0x01, and do a copy from that buffer
to the direct memory, as many times as needed.
    
    Since both of these will make the code much more complex, let's measure to see the cost
of the simple solution before we try them.
    
    Also, at a higher level, we should not even need this trick. A properly-designed value
vector hierarchy would treat a non-nullable vector as a nullable vector that always returns
`false` for `isNull()`. This is what the new readers do and it vastly simplifies the code.
    
    Sometimes it helps to go back to basics and remember Abstractions 101: well-designed abstractions
are our friend.


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