Database Reference
In-Depth Information
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
frequently less than 1 s. There are quite a few limitations which 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
maximum 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 s,
the max query results is 2500 and the maximum query response size is 1 MB.
Amazon Relational Database Service (RDS) is another Amazon service which
gives access to the full capabilities of the familiar MySQL, Oracle and SQL Server
relational database systems. Hence, the code, applications, and tools which 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
software. Amazon RDS can also provide data replication synchronization and
automatic failover management services.
Microsoft SQL Azure
Microsoft has recently released the Microsoft SQL Azure Database system [
44
]
which has been announced as a cloud-based relational database service that has been
built on Microsoft SQL Server technologies [
79
]. 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 across multiple tables, supports aggregation and full-text queries.
It also supports Transact-SQL (T-SQL), native ODBC and ADO.NET data access.
2
In particular, the SQL Azure service can be seen as running an instance of SQL
server in a cloud hosted server which is automatically managed by Microsoft instead
of running on-premise managed server.
In SQL Azure, a logical database is called a
table group
which can be keyless
or keyed. A keyless table group is an ordinary SQL server database where there
are no restrictions on the choices of keys for the tables. On the other hand, if a
table group is keyed, then all of its tables must have a common column called the
partitioning key
which does not need not to be a unique key for each relation. A
row
group
is a set of all rows in a table group that have the same partition key value.
SQL Azure requires that each transaction executes on one table group. If the table
group is keyed, then the transaction can read and write rows of only one row group.
