Database company MySQL has made it harder for developers to use its enterprise software for free. The move has prompted a debate about whether the company has strayed too far from its open-source obligations.

Kaj Arno, MySQL vice president for community, wrote in his blog that the company will no longer host the code for MySQL Enterprise Server in binary form on its public FTP servers, and will offer that version only to paying customers.

The goal is to make it clearer that the enterprise edition is aimed at paying customers, who also receive support and other services, and that another version of the product, MySQL Community Server, is for developers who use the software for free, he said.

The source code for MySQL Enterprise Server will still be freely available from the MySQL Bitkeeper repository, but not as a single, executable file, also known as a "tarball," which means it will take more time and effort to install.

The change conforms with the terms of the open-source GNU General Public License version 2 (GPLv2) that MySQL uses, Arno wrote, "something that we've verified with the Free Software Foundation (FSF) to eliminate any doubt."

Nevertheless, the change sparked criticism. Some developers said MySQL should maintain free access to the enterprise product, since the MySQL community helps to test and develop the software voluntarily. Others argued that MySQL has a right to make business decisions that allow the company to make more money.

The move may comply "technically" with the GPL, "but it doesn't seem to fit with the spirit of open source," MySQL developer Mike Kruckenberg wrote in a blog about the changes. "When I think open source I think freely available source, not source I can get once I've paid for a licence."

He speculated about a "MySQL master plan" to eventually close off the source code for its enterprise product and "cripple" the community edition, forcing all users to pay for the software.

Kevin Burton, CEO of the Internet company Spinn3r, which uses MySQL in its business, said the changes will achieve the opposite of MySQL's goal. "It's just going to make it harder for the Open Source community to work with MySQL and end up pushing them into the hands of PostgreSQL," a rival open-source database, Burton wrote in his blog.

But others were more sanguine.

"I don't see this [being] as much of an issue as some of the open-source zealots and evangelists are making out," said Andrew Poodle, the founder of the UK MySQL user group. "MySQL aren't closing the code, they aren't becoming 'evil', they are just separating out their commercial side of the business from the community side of the business."

The concerns over the changes stem partly from the fact that MySQL introduced new features to the Community Server that made it unstable, Poodle said. The idea was to test and debug the new features before they were added to the enterprise product, but it led to a perception that the enterprise edition is better and more stable.

But MySQL addressed that problem with another part of its announcement this week, Poodle noted. MySQL's Arno wrote that new features will no longer be applied to a current general-availability version of the Community Server, to ensure its stability. Instead, they'll be added to alpha and beta releases of the product.

"MySQL is a business, and I don't believe anyone at the FSF or anyone who supports the GPL would say that making money, even out of open-source software, is wrong," Poodle said.

Arno has responded to the criticisms himself.

"I argue that while this may feel or appear like a step away from open source, the real effect on the core MySQL community member is minuscule," he wrote. "And this is by design. We don't intend for the change to adversely affect core MySQL community members' usage."

He added that the company had "no intention" of moving MySQL Enterprise Server to another licence. "Yes, we are evaluating GPLv3 instead of GPLv2, but our plan is for both Community Server and Enterprise Server to remain GPL," he wrote.