Red Hat has invested an unspecified amount in open source database vendor EnterpriseDB, a sign that the Linux vendor may be worried about the implications of Oracle's takeover of MySQL through its pending acquisition of Sun Microsystems.

The announcement was made in a statement posted by the database vendor.

Neither EnterpriseDB nor Red Hat immediately responded to requests for comment.

The move is notable because much of Red Hat's current popularity as a server platform is due to users looking to run the free MySQL on top of Red Hat as part of a LAMP (Linux, Apache, MySQL, Python/Perl/PHP) server. EnterpriseDB sells a proprietary, Oracle-compatible database called PostgresPlus that is based around the open source PostgreSQL technology.

The two companies had reportedly been edging towards each other for months. EnterpriseDB CEO Ed Boyajian is also a former Red Hat vice president.

Boyajian, quoted by CNET news, said that the investment, part of a $19 million Series C round of funding, was a "significant amount of money."

EnterpriseDB took a small investment from IBM a year and a half ago, as part of its move away from Sun Microsystems, which at that time had just acquired MySQL. This time around, fears about the fate of MySQL after Oracle's takeover may have motivated Red Hat to hedge its bets by getting cozy with EnterpriseDB, said Gordon Haff, an analyst with Illuminata.

Despite Oracle's promises to the contrary , some fear that Oracle will bury or weaken MySQL to prevent it from cannibalising sales of the pricier Oracle Database.

Asay theorised that Red Hat's investment is a counterattack of sorts, pumping up EnterpriseDB as a low cost challenger to Oracle and other expensive proprietary databases.

Though far less widely used than MySQL, the PostgreSQL that EnterpriseDB relies upon is also generally considered more suitable for large, enterprise workloads than MySQL. EnterpriseDB has had some success pulling away Oracle customers, claiming 225 paying customers as of its investment by IBM in March 2008.

Read Martin Veitch's analysis of the deal here.