Split size is the number of regions that are on this server that all are
of the same table, squared, times the region flush size OR the maximum
region split size, whichever is smaller. For example, if the flush size
is 128M, then on first flush we will split which will make two regions
that will split when their size is 2 * 2 * 128M = 512M. If one of these
regions splits, then there are three regions and now the split size is
3 * 3 * 128M = 1152M, and so on until we reach the configured
maximum filesize and then from there on out, we'll use that.