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no index maintenance work of any kind to do. On the other side, the user does not
have any direct control over the created indices. SimpleDB provides a small group of
API calls that enables the core functionality for building client applications such as
CreateDomain , DeleteDomain , PutAttributes , DeleteAttributes , and GetAttributes.
The SimpleDB API also provides a query language that is similar to the SQL Select
statement. Hence, this query language makes SimpleDB Selects very familiar to
the typical database user that ensures a gentle learning curve. However, it should
be noted that the language supports issuing queries only over the scope of a single
domain (no joins, multidomain, or subselect queries).
SimpleDB is implemented with complex replication and failover mechanisms
behind the scenes. Therefore, it can provide a high availability guarantee with the
stored data replicated to different locations automatically. Hence, a user does not
need to make any extra effort or become an expert on high availability or the details
of replication techniques to achieve the high availability goal. SimpleDB supports
two options for each user read request: eventual consistency or strong consistency.
In general, using the option of a consistent read eliminates the consistency window
for the request. The results of a consistent read are guaranteed to return the most
up-to-date values. In most cases, a consistent read is no slower than an eventually
consistent read. However, it is possible for consistent read requests to show higher
latency and lower bandwidth on some occasions (e.g., high workloads). SimpleDB
does not offer any guarantees about the eventual consistency window but it is fre-
quently less than one second. There are quite a few limitations that a user needs to
consider while using the simpleDB service such as the maximum storage size per
domain is 10 GB, the maximum attribute values per domain is 1 billion, the maxi-
mum attribute values per item is 256, the maximum length of item name, attribute
name, or value is 1024 bytes, the maximum query execution time is 5 seconds, the
max query result is 2500, and the maximum query response size is 1 MB.
Amazon Relational Database Service (RDS) is another Amazon service that
gives access to the full capabilities of the familiar MySQL, Oracle, and SQL Server
relational database systems. Hence, the code, applications, and tools that are already
designed on existing databases of these system can work seamlessly with Amazon
RDS. Once the database instance is running, Amazon RDS can automate common
administrative tasks, such as performing backups or patching the database soft-
ware. Amazon RDS can also provide data replication synchronization and automatic
failover management services.
9.4.3 m iCrosoFt sQl a zure
Microsoft has recently released the Microsoft SQL Azure Database system,* which
has been announced as a cloud-based relational database service that has been built
on Microsoft SQL Server technologies [12]. It provides a highly available, scalable,
multi-tenant database service hosted by Microsoft in the cloud. So, applications can
create, access, and manipulate tables, views, indexes, referential constraints, roles,
stored procedures, triggers, and functions. It can execute complex queries, joins
* http://www.microsoft.com/windowsazure/sqlazure/.