I have a cluster using HBase 1.1.2 where I have a table and a local index (using Apache Phoenix 4.6) in total both tables have 300 regions (aprox: 18 regions per server), myhbase.hregion.max.filesize=30GBand my region sizes are now ~4.5GB compressed (~7GB uncompressed). However each time I restart a RS sometimes a region gets split. This is unexpected because my key space is uniform (using MD5) and if the problem was my region.size > hbase.hregion.max.filesize I would expect to have all the regions or almost all splitting but this only happens when I restart a RS and it happens only for 1 or 2 regions.
What are the different scenarios where a region can split?
What are the right steps to restart a region server in order to avoid these unexpected splits?