Hector is a high-level client
API
An application programming interface (API) is a way for two or more computer programs to communicate with each other. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how ...
for
Apache Cassandra
Cassandra is a free and open-source, distributed, wide-column store, NoSQL database management system designed to handle large amounts of data across many commodity servers, providing high availability with no single point of failure. Cassand ...
. Named after
Hector
In Greek mythology, Hector (; grc, Ἕκτωρ, Hektōr, label=none, ) is a character in Homer's Iliad. He was a Trojan prince and the greatest warrior for Troy during the Trojan War. Hector led the Trojans and their allies in the defense o ...
, a warrior of
Troy
Troy ( el, Τροία and Latin: Troia, Hittite: 𒋫𒊒𒄿𒊭 ''Truwiša'') or Ilion ( el, Ίλιον and Latin: Ilium, Hittite: 𒃾𒇻𒊭 ''Wiluša'') was an ancient city located at Hisarlik in present-day Turkey, south-west of Ç ...
in
Greek mythology
A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the lives and activities ...
, it is a substitute for the Cassandra Java Client, or Thrift,
that is encapsulated by Hector. It also has
Maven
MAVEN is an American spacecraft orbiting Mars to study the loss of its atmospheric gases to space, providing insight into the history of
the planet's climate and water. The spacecraft name is an acronym for "Mars Atmosphere and Volatile Evolu ...
repository access.
History
As Cassandra is shipped with the low-level
Thrift (protocol)
Thrift is an interface definition language and
binary communication protocol
used for defining and creating services for numerous programming languages. It was developed at Facebook for "scalable cross-language services development" and as of ...
, there was a potential to develop a better protocol for application developers. Hector was developed by Ran Tavory as a high-level interface that overlays the shortcomings of Thrift. It is licensed with the MIT License that allows to use, modify, split and change the design.
Features
The high-level features of Hector are
* A high-level object oriented interface to Cassandra: It is mainly inspired by the Cassandra-java-client. The API is defined in the Keyspace interface.
* Connection pooling. As in high-scale applications, the usual pattern for
DAO
Dao, Dão or DAO may refer to:
* Tao (Chinese: "The Way" 道), a philosophical concept
* Dao (Chinese sword) (刀), a type of Chinese sword
* Dao (Naga sword), a weapon and a tool of Naga people
People and language
* Yao people, a minority ethni ...
s is a large number of reads/writes. It is too expensive for clients to open new connections with each request. So, a client may easily run out of available sockets, if it operates fast enough. Hector provides connection pooling and a nice framework that manages the details.
* Failover support: As Cassandra is a distributed data store where hosts (
''nodes'') may go down. Hector has its own
failover policy.
*
JMX support: Hector exposes JMX for many important runtime metrics, such as number of available connections, idle connections, error statistics.
*
Load balancing: A simple load balancing exists in the newer version.
* Supports the command design pattern to allow clients to concentrate on their business logic and let Hector take care of the required plumbing.
Availability metrics
Hector exposes availability counters and statistics through
JMX.
Load balancing
Hector follows two load balancing policies with the
LoadBalancingPolicy interface. The default is called
RoundRobinBalancingPolicy and is a simple
round-robin distribution algorithm. The
LeastActiveBalancingPolicy routes requests to the pools having the lowest number of active connections, ensuring a good spread of utilisation across the cluster. .
Pooling
The
ExhaustedPolicy determines how the underlying client connection pools are controlled. Currently, three options are available:
Code examples
As an example, an implementation of a simple distributed
hashtable
In computing, a hash table, also known as hash map, is a data structure that implements an associative array or dictionary. It is an abstract data type that maps keys to values. A hash table uses a hash function to compute an ''index'', also ...
over Cassandra is listed.
/**
* Insert a new value keyed by key
* @param key Key for the value
* @param value the String value to insert
*/
public void insert(final String key, final String value) throws Exception
/**
* Get a string value.
* @return The string value; null if no value exists for the given key.
*/
public String get(final String key) throws Exception
/**
* Delete a key from cassandra
*/
public void delete(final String key) throws Exception
References
External links
Apache ThriftHector on githubThe Cassandra Java client
{{DEFAULTSORT:Hector (Api)
Distributed computing
Distributed data stores
Java (programming language)