Google App Engine is a platform for building and hosting web applications on Google Web Servers. It was first released as a beta version in April 2008. During its preview release, only free accounts are offered. According to Google, a free account can use up to 500 MB of persistent storage and enough CPU and bandwidth for about 5 million page views a month. Google has also indicated its intention to eventually provide additional resources for a price. During the preview stage, Google App Engine tries to accommodate sudden surges in traffic, but errors will occur if the quota continues to be exceeded.

Supported programming languages and frameworks

At its launch date, the only supported programming language was Python. A limited version of the Django web framework is available, as well as a custom Google-written web app framework similar to JSP or ASP.NET. Google has said that it plans to support more languages in the future. Any Python framework not requiring network access, data storage outside the Google Datastore, file system access, or compiled Python modules written in C or Pyrex should work on the Google App Engine.

Differences from traditional application hosting

Unlike more traditional virtual-machine setups such as Amazon’s EC2, Joyent’s Accelerator, FlexiScale, or even a simple shared server or dedicated server system, App Engine is a tightly controlled and tightly integrated product that places many restrictions on users. While others allow for the installation and configuration of nearly any *NIX compatible software, AppEngine requires developers to use Python as the programming language and “Datastore” – a version of Google’s proprietary BigTable – for data persistence.

Scalability benefits gained from removing joins

Google App Engine has a SQL-like syntax called “GQL”. Select statements in GQL can be performed on one table only. GQL intentionally does not support the Join statement.

One-to-many relationships and many-to-many relationships can be accomplished using ReferenceProperty(). This shared-nothing approach allows disks to fail without the system failing.

The where clause of select statements can perform >, >=, <, <= operations on one column only. Therefore, only simple where clauses can be constructed. Switching from a relational database to the Datastore requires a paradigm shift for developers when modeling their data.

App Engine limits the maximum rows returned from an entity get to 1000 rows per Datastore call. Most web database applications use paging and caching, and hence do not require this much data at once, so this is a non-issue in most scenarios.[citation needed] If an application needs more than 1,000 records per operation, it can use its own client-side software or an Ajax page to perform an operation on an unlimited number of rows.

Task scheduling is a heavily requested feature by App Engine users for future releases. Batch updates that take longer than a few seconds cannot be executed. Many have speculated that once the free quota restrictions are lifted, Google will introduce support for such operations. However, mapreduce operations are now supported.

Unlike a relational database such as Oracle, Microsoft SQL Server, MySQL, or PostgreSQL, the Datastore API is not relational in the SQL sense.

Restrictions

• Developers have read-only access to the filesystem on App Engine.
• App Engine can only execute code called from an HTTP request.
• No support for task scheduling in the traditional sense.
• Users may upload arbitrary Python modules, provided they are pure-Python. C and Pyrex modules are not supported.

Competition

The service competes with Amazon Web Services, a set of application services that enable web sites to host files and execute code on Amazon’s servers. Many tech analysts have been predicting Google’s entry into this field for years. “Google finally realizes it needs to be the web platform,” Techdirt publisher Mike Masnick wrote. “The easier it is to develop and deploy highly scalable web applications, the more innovative and creative solutions we’re going to start to see.”

Other competitors include Microsoft’s Azure Services Platform.

Links

• Official site
• Best Enterprise Startup Crunchies 2008

Tags: accelerator, amazon, amazon web, Google, Google App Engine, microsoft, software, Top, web service

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