History[05]

HBase was initially a project by the company Powerset, a San Francisco-based search and natural language company. Microsoft acquired Powerset in 2008.

Checkpoints[06]

HBase Snapshots allows the users to make checkpoints of a table with little impact on RegionServers. Creating snapshots does not block reads and writes, but for each table only one snapshot can be created at a time.

Concurrency Control[07]

HBase guarantees ACID semantics per-row. HBase uses a form of Multiversion Concurrency Control (MVCC) to avoid row locks for read operations. Write operations still need to acquire row locks.

Data Model[08]

An HBase table consists of rows and columns. Rows are referenced by row keys which are raw byte arrays and are sorted by row key. The sort is byte-ordered. Each row contains columns. A column's content is also an uninterpreted array of bytes. All columns belong to a column family.

Foreign Keys[09]

HBase does not directly support refential integrity. Users can use a coprocessor to enforce foreign keys.

Indexes[10]

For each table, HBase only provide an B+Tree like index on row keys. HBase does not natively support secondary indexes. Users can use filters for querying on non-rowkey columns. There are some techniques to create another table which can be used as a secondary index.

Isolation Levels[11][12]

HBase only provide "read committed" isolation level. Users can downgrade the isolation level to "read uncommitted" by modifying the source code.

Joins[13]

HBase does not support join operations. Users can implement joins in their application code.

Logging[14][15]

HBase's write-ahead-log is named HLog.

Query Compilation

Query Execution[16]

Query Interface[17]

HBase does not provide native support for SQL. Unlike RDBMS, HBase has four primary operations: Get, Put, Scan and Delete. It also has some DDL operations, e.g., Create. HBase provides a shell which users can fire queries from. Users can specify table name, column names and apply filters in their query. HBase also offers Java Client API and Thrift/REST API. Some third-party drivers are also available for other programming languages.

Storage Architecture[01]

HBase leverages HDFS as the backend storage. Currently HDFS is disk-oriented.

Storage Model[18][19]

HBase is schema-less column-oriented datastore.

Stored Procedures[20]

Stored procedures are not directly supported in HBase. But users can use coprocessors to resemble store procedures.

System Architecture[21][22]

HBase is organized as a cluster of HBase nodes that complies with the master-slave architecture. There are two types of nodes: a master node, and one or more slave nodes called RegionServers. RegionServers serve data for reads and writes. An HBase Region is a subset of an HBase table that has a continuous range of sorted rowkeys. Region assignment and DDL operations are handled by the HBase Master. HBase is built on top of Hadoop File System, thereby making it shared-disk. The Hadoop DataNodes store the data that RegionServers are managing. The HDFS Zookeeper maintains the server status in the cluster.

Views[23]

HBase does not provide views. But users can write MapReduce programs to approximate views. Apache Phoenix, a SQL interface for HBase, provides support for views.