EnterpriseDB on Tuesday announced that it had raised $US10 million from funders including IBM , which took a small but symbolically laden stake in the 4-year-old open-source database maker.

EnterpriseDB's products are based around the open-source PostgreSQL technology, a rival to the more popular MySQL. For several years, Sun Microsystems had been one of the strongest supporters of PostgreSQL, bundling it with its Solaris 10 operating system, and partnering with EnterpriseDB to provide support.

Sun bought MySQL AB in late January. Though Sun and EnterpriseDB executives both denied at the time that Sun's backing for PostgreSQL would weaken, EnterpriseDB CEO, Andy Astor, admitted in an interview last week that he no longer "has high expectations for Sun and Postgres."

"We will continue to have a relationship with Sun and we will continue to support Postgres [for Sun], but frankly, if I paid $1 billion for MySQL, I know where I'd be paying attention," Astor said.

IBM, meanwhile, is "very interested" in what EnterpriseDB is doing, Astor said. The company joins Charles River Ventures, Fidelity Ventures and Valhalla Partners in this Series C funding round.

IBM did not return a request for comment. But Raven Zachary, an analyst with The 451 Group, said the investment "is a significant move."

"With MySQL as part of Sun now, IBM sees its open source database future aligned with PostgreSQL through EnterpriseDB," he wrote in an email. "IBM also gains in this move through EnterpriseDB's Oracle database compatibility, as IBM competes with Oracle via DB2. This is a smart move for IBM."

EnterpriseDB has now raised a total of $37.5 million in its four-year history. It claims 225 paying customers today. Asked why IBM did not simply buy EnterpriseDB, Astor answered, "because we're not for sale."

The company already provides a version of its database for IBM's Z/OS mainframe platform. Astor said similar marketing partnerships with other partners are in the offing.

He also had no reservations about aiming a few polemical blasts at EnterpriseDB's rival.

"We are going straight after MySQL in the marketplace with a dramatically more robust database," he said. EnterpriseDB "has excellent tooling, is faster than MySQL in transactional environments and is far more scalable."

He continued: "If it was going to cost the same to get either a Yugo or a Mercedes, which one would you pick?"

MySQL actually has a partnership with IBM, with its database bundled into IBM's System i servers.

Zachary doesn't think IBM will abandon that.

"It's in IBM's best interests to make sure the most popular open source software works on its systems, and that includes MySQL. I wouldn't read too much into this," he said.

EnterpriseDB is one of the largest contributors of source code back to the PostgreSQL project. But much of what EnterpriseDB sells is a set of extensions on top of PostgreSQL. The company doesn't assign those extensions back to the project. As such, it has been tarred by purists as one of several essentially closed-source companies operating in the guise of open-source firms.

Perhaps in reaction to those concerns, EnterpriseDB also today announced the release of its open-source Postgres Plus 8.3, which is based on PostgreSQL but includes some of EnterpriseDB's improvements. EnterpriseDB will still offer an Advanced Server version of Postgres Plus that is neither free nor open-source, but includes Oracle compatibility and other features.

EnterpriseDB is also making its GridSQL data warehousing software available immediately under the General Public License version 2.0.

"I think that EnterpriseDB's product rebranding clarifies some ambiguity that existed in the market," Zachery said.