private void updateAvgVariableSize(VectorizedRowBatch batch) {
      int keyVariableSize = keyWrappersBatch.getVariableSize(batch.size);
      int aggVariableSize = aggregationBatchInfo.getVariableSize(batch.size);

      // This assumes the distribution of variable size keys/aggregates in the input
      // is the same as the distribution of variable sizes in the hash entries
      avgVariableSize = (int)((avgVariableSize * sumBatchSize + keyVariableSize +aggVariableSize) /
          (sumBatchSize + batch.size));
    }
Updates the average variable size of the hash table entries.
The average is only updates by probing the batch that added the entry in the hash table
that caused the check threshold to be reached.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorGroupByOperator.java