HBase is a horizontally scalable, distributed, open source, and a sorted map database. It runs on top of Hadoop file system that is Hadoop Distributed File System (HDFS). HBase is a NoSQL nonrelational database that doesn't always require a predefined schema. It can be seen as a scaling flexible, multidimensional spreadsheet where any structure of data is fit with on-the-fly addition of new column fields, and fined column structure before data can be inserted or queried. In other words, HBase is a column-based database that runs on top of Hadoop distributed file system and supports features such as linear scalability (scale out), automatic failover, automatic sharding, and more flexible schema.
HBase is modeled on Google BigTable. It was inspired by Google BigTable, which is compressed, high-performance, proprietary data store built on the Google file system. HBase was a developed as a Hadoop subproject to support storage of structural data, which can take advantage of most distributed files systems (typically, the Hadoop Distributed File System known as HDFS).
The following table contains key information about HBase and its features:
|
Features |
Description |
|---|---|
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Developed by |
Apache |
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Written in |
Java |
|
Type |
Column oriented |
|
License |
Apache License |
|
Lacking features of relational databases |
SQL support, relations, primary, foreign, and unique key constraints, normalization |
|
Website | |
|
Distributions | |
|
Download link | |
|
Mailing lists |
|
|
Blog |
The following figure represents the layout information of HBase on top of Hadoop:
There is more than one ZooKeeper in the setup, which provides high availability of master status; a RegionServer may contain multiple rations. The RegionServers run on the machines where DataNodes run. There can be as many RegionServers as DataNodes. RegionServers can have multiple HRegions; one HRegion can have one HLog and multiple HFiles with its associate's MemStore.
HBase can be seen as a master-slave database where the master is called HMaster, which is responsible for coordination between client application and HRegionServer. It is also responsible for monitoring and recording metadata changes and management. Slaves are called HRegionServers, which serve the actual tables in form of regions. These regions are the basic building blocks of the HBase tables, which contain distribution of tables. So, HMaster and RegionServer work in coordination to serve the HBase tables and HBase cluster.
Usually, HMaster is co-hosted with Hadoop NameNode daemon process on a server and communicates to DataNode daemon for reading and writing data on HDFS. The RegionServer runs or is co-hosted on the Hadoop DataNodes.