IBM is offering an annual support option for the free version of its DB2 database, the first of the top three database vendors to make such a move.

Customers using IBM's DB2 Express-C database can now buy a one-year subscription for the software, including support, for US$2,995 (£1,495) before tax, according to IBM's website.

Customers who buy a subscription for two servers can build a high-availability configuration using clustering or the High Availability Disaster Recovery feature, without having to buy additional software, IBM said. The subscription also includes around-the-clock technical support, maintenance and upgrades.

IBM, Oracle and Microsoft each offer a free version of their databases, which have been seen as a way to ward off competition from open-source rivals. They each come with usage restrictions, however. IBM's is designed for use on servers with up to 4GB of main memory and one or two dual-core x86 processors, or two cores of any other type of processor. IBM does not limit the amount of data that can be stored in the database.

Four gigabytes of main memory "should be about enough for most medium-sized businesses," said Ovum analyst David Mitchell.

Open-source companies such as MySQL AB already offer a free database with optional support, Mitchell noted. The new support service from IBM is not a dramatic change for the market, therefore, although it could prompt Microsoft and Oracle to follow suit, he said.

Leon Katnelson, a program director with IBM's DB2 division, discussed the support offering in a posting at IBM's DB2 Express Forum. Customers receive product keys that turn their Express-C database into a supported product that can be used for data replication and deployed within clusters, he said.

"For a DB2 Express-C server to participate in a data replication scenario as either the source or the destination, the DB2 Express-C server MUST have a valid subscription enabled," he wrote.

The maintenance support includes quarterly FixPaks, but they cannot be applied to Express-C servers that are not covered by subscription, Katnelson said.

The subscription service is available worldwide, according to an IBM spokeswoman. IBM officially announced the service on Thursday, although Katnelson discussed it in his database blog on Tuesday.