Well, boys, there’s a new database gun in town.

NorthScale, the start-up du jour, broke cover Tuesday brandishing the premise that your traditional RDBMS ain’t what you want for web application data.

Instead it’s got some free – as well as paid – scale-out data management widgetry that it calls “elastic data infrastructure,” built by the primary contributors and committers to the Memcached open source project – (which, it will point out, is used by 18 of the top 20 most heavily trafficked web sites).

NorthScale’s memcached distribution is designed to scale horizontally and infinitely, working alongside existing RDBMSs to provide data management that’s simple, non-disruptive and cost-effective for modern web applications.

It’s supposed to match the scale-out needs and architecture of modern web applications and compute clouds, and promises substantial reductions in capital and operating costs.

Described as optimized for web applications and cloud computing, its solution is already being leveraged by web properties such as Zynga’s FarmVille, Café World, Mafia Wars and other games that have over 235 million active users a month as well as Korea’s number one search portal, Naver.com, a $1.2 billion operation.

NorthScale observes that web applications generate data at volumes exceeding any other category of interactive software – and waves around IDC estimates that in 2012 the amount of digital information produced a year will equal nearly 2,500 exabytes, thanks to the Internet, which is 2,500 billion gigabytes or five times what was produced in 2008.

And a lot of this data, and the interaction patterns between the software and data, it says, differs fundamentally from those of transactional software systems such as the payroll and ERP widgetry beloved by your average RDBMS. But despite the differences, relational database technology continues to be used as a “one size fits all” approach for both classes of software.

This is where NorthScale comes in.

It says you can forget the ACID guarantees of relational databases, and their cost and scalability limitations, along with what NorthScale co-founder and chief strategy officer James Phillips calls their “intolerable overkill,” and substitute the start-up’s distributed key-value cache and database technologies.

It says users can start with existing relational database technology and expertise, and incrementally evolve towards a scale-out data architecture for their web applications using its Memcached Server and Membase Server.

The freebie NorthScale Memcached Server is an enhanced memcached distribution that features secure application multi-tenancy (it supports multiple applications on a shared cluster); dynamic cluster scaling; browser-based cluster administration (to monitor and manage a memcached cluster); 100% “memcapable” certification (meaning it supports all protocols and operations); and support for Linux and Windows (Windows ain’t usual).

The paid NorthScale Membase Server, on the other hand, is a high-performance distributed key-value database that builds on the server and persists the data, something memcached doesn’t do. It can also replicate data and promises down the line to index and query. Compatible with memcached APIs and existing client libraries, it can be the primary database rather than an RDBMS.

While memcached reduces the number of reads an application must do from the database – because of its distributed in-memory caching technology of course – data is still inevitably stored in a relational database. NorthScale says using its Membase Server an organization can identify and gradually “drain” data from a relational system to Membase and get the “simple, fast and infinite properties” of memcached across both reads and writes, while slashing data management costs.

This widgetry offers a distributed key-value database for storing data objects; supposedly infinite scalability – just add more commodity servers, NorthScale says, to expand data and I/O capacity; extremely high-performance (the speed of memcached for both reads and writes); tunable persistence behavior (optimize write patterns to match application needs); a pluggable storage engine to store data on- or off-node with user-replaceable storage subsystems; and fully configurable data replication (think data-layer fault tolerance for continuous application ops).

Subscription-based pricing for support for its Memcached Server starts at $799/server/year and runs to $1.299 depending on the support level.

The Membase Server is currently deployed in private beta with three customers and has already brought in $500,000 according to Phillips. It will be available for public beta testing in a couple of months. Product availability and pricing will be announced in Q2.

There’s also a free downloadable Developer Kit.

NorthScale started to get organized in January of ’09 and picked up $5 million in funding soon after from Accel Partners and North Bridge Venture Partners. It’s got less