A region will not split, if there is already a set of "reference files". A reference file is a soft link to "half of" some other hfile. When a region splits, there would be two daughter regions, which have these reference files, referring to the parent. This scheme ensures that region splits are quick, and never re-writes the entire region data during the split. A region will NEVER split if there are reference files lying around still referring to its parents. Reference files normally get cleaned out by compaction. Once the compaction re-writes the file, the reference files will be deleted and the region can split again. If you use case bulk loads every 10 seconds or so, then there is probably A LOT Of small files being written and immense compaction pressure resulting in compactions not going through, and hence blocking further splits in the region. I recommend reducing the frequency of bulk loads, optimizing compaction file limits to be higher and in general keeping the compaction queue not full.
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