public VectorHashKeyWrapperBase allocateKeyWrapper() {
    return VectorHashKeyWrapperFactory.allocate(hashCtx,
        longIndices.length,
        doubleIndices.length,
        stringIndices.length,
        decimalIndices.length,
        timestampIndices.length,
        intervalDayTimeIndices.length,
        keyCount);
  }
Prepares a VectorHashKeyWrapperBatch to work for a specific set of keys.
Computes the fast access lookup indices, preallocates all needed internal arrays.
This step is done only once per query, not once per batch. The information computed now
will be used to generate proper individual VectorKeyHashWrapper objects.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/wrapper/VectorHashKeyWrapperBatch.java