Understanding HBase RegionServer, HRegion, HStore, and Column Family Management

HRegionServer internally manages a series of HRegion objects, each corresponding to a region in a table; each HRegion consists of multiple HStore instances.

Each HStore corresponds to a column family in the table, acting as a dedicated storage unit, so column families with similar I/O characteristics should be grouped together for maximum efficiency.

HStore storage is the core of HBase storage and comprises two parts: MemStore and StoreFile. MemStore is a sorted memory buffer where incoming writes are first stored; when MemStore fills up, it is flushed to a StoreFile (implemented as an HFile).

The condition for splitting a region is that the largest StoreFile among all stores in the region exceeds a predefined threshold.

At the file level, different column families are stored in separate files, but multiple column families can share the same region.

For example, the following paths show two different column families sharing the same region /hbase/zz/3917ebd872c0adcb9d6c5a9cfd30b87f/a and /hbase/zz/3917ebd872c0adcb9d6c5a9cfd30b87f/b.

Because column families share a region, a situation may arise where one column family contains millions of rows while another has only a few; when a region split is triggered, the small column family is also split across many regions, leading to a cardinality problem and degraded scan performance.

Additionally, flushing one column family can cause neighboring column families to flush due to coupling effects, increasing I/O.

Therefore, it is generally recommended not to define multiple column families in a table.