Chapter 14. Too Many Regions
Having too many regions can impact your HBase application in many ways.
The most common consequence is related to HFile compactions. Regions are sharing the memstore memory area. Therefore, the more regions there are, the smaller the memstore flushes will be. When the memstore is full and forced to flush to disk, it will create an HFile containing data to be stored in HDFS. This means the more regions you have, the smaller the generated HFiles will be. This will force HBase to execute many compaction operations to keep the number of HFiles reasonably low. These compactions will cause excessive churn on the cluster, affecting performance. When specific operations are triggered (automatic flush, forced flush, and user call for compactions), if required, HBase will start compactions. When many compactions run in tandem, it is known as a compaction storm.
Compactions are normal HBase operations. You should expect them, and there is nothing to worry about when minor compactions are running. However, it is recommended to monitor the number of compactions. The compaction queue should not be constantly growing. Spikes are fine, but the key needs to stay close to zero most of the time. Constant compactions can be a sign of poor project design or a cluster sizing issue. We call constant compactions a situation where the compaction queue for a given RegionServer never goes down to zero or is constantly growing.
Certain operations can timeout ...