@Override
  public String toString() {
    return "IncreasingToUpperBoundRegionSplitPolicy{" + "initialSize=" + initialSize + ", "
      + super.toString() + '}';
  }
Split size is the number of regions that are on this server that all are of the same table,
cubed, times 2x the region flush size OR the maximum region split size, whichever is smaller.
<p>
For example, if the flush size is 128MB, then after two flushes (256MB) we will split which will
make two regions that will split when their size is {@code 2^3 * 128MB*2 = 2048MB}.
<p>
If one of these regions splits, then there are three regions and now the split size is
{@code 3^3 * 128MB*2 = 6912MB}, and so on until we reach the configured maximum file size and
then from there on out, we'll use that.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/IncreasingToUpperBoundRegionSplitPolicy.java