The components of a Region Server are:
- WAL: Write Ahead Log (WAL) is a file attached to every Region Server inside the distributed environment. The WAL stores the new data that hasn’t been persisted or committed to the permanent storage.
- Block Cache: Block Cache resides in the top of Region Server. It stores the frequently read data in the memory.
- MemStore: It is the write cache. It stores all the incoming data before committing it to the disk or permanent memory. There is one MemStore for each column family in a region.
- HFile: HFile is stored in HDFS. It stores the actual cells on the disk.
