New Relic, a company that focuses on helping Rails developers optimize and maintain their code, has closed a $6 million Series B funding round led by Trinity Ventures, with existing investor Benchmark Capital also participating. After a $3.5 million Series A round earlier this year, the round brings New Relic’s total funding to around $9.5 million. As part of the deal Trinity’s Dan Scholnick will be joining the New Relic board, with Benchmark Capital’s Peter Fenton taking the role of chairman of the board.

New Relic offers subscription-based services for developers using the popular Ruby on Rails platform. The company’s Rails Performance Management (RPM) package helps developers test their code for performance issues, presenting data in an intuitive graphical interface. To use the service, developers install the RIM Rails plug-in into their project, which then relays the data to New Relic’s servers for analysis (you can see our full post on the service here).

Since its launch earlier this year, the site has racked up an impressive list of customers, including 37signals and Github (a well-known collaborative development tool). Its initial success isn’t surprising – the site was founded by Lewis Cirne, who created a similar service for Java developers in the late 90′s that was eventually acquired (a number of his coworkers from that endeavor have joined him on the new project).

Another player in this space (also focused on Ruby on Rails) is FiveRuns.