An Overview of the NoSQL World - Large Scale and Big Data: Processing and Management - page 298

guarantees in a way that a process could read an old version of a document even if
another process has already performed an update operation on it. In addition, it pro-
vides no transaction management so that if a process reads a document and writes a
modified version back to the database, there is a possibility that another process may
write a new version of the same document between the read and the write operation
of the first process. MongoDB supports indexing the documents on multiple fields. In
addition, it provides a very rich API interface that supports different batch operations
and aggregate functions.
Many other variant projects have followed the NoSQL movement and support
different types of data stores such as key-value stores (e.g., Voldemort,* Dynomite † ),
document stores (e.g., Riak ‡ ), and graph stores (e.g., Neo4j, § DEX ¶ ).
9.4 DATABASE-AS-A-SERVICE
Multitenancy , a technique which is pioneered by salesforce.com , ** is an optimization
mechanism for hosted services in which multiple customers are consolidated onto the
same operational system and thus the economy of scale principles help to effectively
drive down the cost of computing infrastructure. In particular, multitenancy allows
pooling of resources that improves utilization by eliminating the need to provision
each tenant for their maximum load. Therefore, multitenancy is an attractive mecha-
nism for both of the service providers who are able to serve more customers with a
smaller set of machines, and also to customers of these services who do not need to
pay the price of renting the full capacity of a server. Database-as-a-service (DaaS) is
a new paradigm for data management in which a third-party service provider hosts a
database as a service [3,37]. The service provides data management for its customers
and thus alleviates the need for the service user to purchase expensive hardware and
software, deal with software upgrades, and hire professionals for administrative and
maintenance tasks. Since using an external database service promises reliable data
storage at a low cost, it represents a very attractive solution for companies especially
that of startups. In this section, we give an overview of the state-of-the-art of differ-
ent options of DaaS from the key players Google, Amazon, and Microsoft.
9.4.1 g oogle D atastore
Google has released the Google AppEngine datastore, †† which provides a scalable sche-
maless object data storage for web application. It performs queries over data objects,
known as entities . An entity has one or more properties where one property can be a
reference to another entity. Datastore entities are schemaless where two entities of the
same kind are not obligated to have the same properties, or use the same value types
* http://project-voldemort.com/.
† http://wiki.github.com/cliffmoon/dynomite/dynomite-framework.
‡ http://wiki.basho.com/display/RIAK/Riak.
§ http://neo4j.org/.
¶ http://www.dama.upc.edu/technology-transfer/dex.
** http://www.salesforce.com/.
†† http://code.google.com/appengine/docs/python/datastore/.