After a decade as chief technology officer at DoubleClick – the internet ad giant he cofounded in 1995 – Dwight Merriman set out to build a "platform cloud" along the lines of Google App Engine or Microsoft Azure. But this was before people called them platform clouds, before anyone knew about App Engine or Azure.
It was late 2007, and the idea was to create an online service for developing, hosting, and automatically scaling web applications. "What we were building was very similar to what App Engine eventually became," Merriman tells us. But unlike App Engine, the service would be underpinned by an entirely open source software stack, and somewhere along the way Merriman and his team realized that no open source database platform was suited to such a service.
"We felt like a lot of existing databases didn't really have the 'cloud computing' principles you want them to have: elasticity, scalability, and ... easy administration, but also ease of use for developers and operators," Merriman says. "[MySQL] doesn't have all those properties."
So they set out to build a database of their own, one that would discard the familiar relational database model in favor of a distributed platform tailored for moden-day web applications. "By reducing transactional semantics, we could still solve an interesting set of problems, but we could also scale," Merriman explains. After a year of work, the database was in place, and they decided it had as much potential as the cloud service it was designed for – if not more. The cloud service was never finished. But the database was open sourced as MongoDB.
Dwight Merriman and his team, including ShopWiki founder Eliot Horowitz, built MongoDB under the aegis of the New York–based startup 10gen, and the company now offers support, training, and consulting services for the database in addition to serving as the open source project's primary steward. This week, 10gen held its second annual San Francisco developer conference, and with his Tuesday-morning keynote, Merriman described the origins of MongoDB and explained why the database was built the way it was.
The split from the relational model was essential, Merriman says, because you can't do distributed joins in a way that readily scales. "I'm not smart enough to do distributed joins that scale horizontally, widely, and are super fast. You have to choose something else," Merriman explained during his talk. "We have no choice but to not be relational."
It was equally important, he says, to limit the database's transactional semantics. "You can do distributed transactions, but if you do them with no loss of generality and you do them across a thousand machines, it's not going to be that fast."