Oracle's recent release of three new commercial extensions to the MySQL database has caused an outcry among some in the MySQL community. Some, including project founder Michael "Monty" Widenius, are concerned that Oracle, by moving to an "open core" model, will slowly move more and more of the database project to commercially licensed code—and to licensing terms that make it difficult for users to escape.

Ulf Sandberg, CEO of SkySQL, a year-old firm made up largely of former MySQL AB employees that offers a subscription-based support for enterprise MySQL users that competes with Oracle's, believes Oracle risks cutting itself off from the community by taking more of the project to a commercial model. "We think they might actually 'fork' themselves," Sandberg tells Ars, as the MySQL user base resists signing on for Oracle's more onerous licensing and moves away from MySQL Enterprise toward alternative releases.

The MySQL community, one of the underpinnings of the open-source LAMP development platform, has already spawned a number of forked-off projects, including: Drizzle, a lightweight MySQL alternative derived the now-deleted MySQL 6.0 development tree by a team led by former MySQL director of architecture Brian Aker; Percona Server , a high-performance version of MySQL based on the XtraDB engine, maintained by former MySQL performance engineer Peter Zaitsev's Percona; and MariaDB, a fork of MySQL 5.1 driven by Widenius' Monty Program Ab that can use the XtraDB or InnoDB storage engines.

Both the Percona Server and MariaDB projects try to cleave closely to MySQL Enteprise's features to maintain compatibility. But as Oracle introduces more commercial code into the MySQL Enterprise subscription version, it will become increasingly difficult to maintain compatibility feature-to-feature.

The commercial licensing trend started well before Oracle acquired MySQL along with the rest of Sun Microsystems, as did the MySQL diaspora. Sun made the decision to release MySQL Enterprise Backup and future new features as commercial code in 2008, a move that created a similar uproar among sectors of the MySQL community. Two commercial extensions, MySQL Enterprise Backup and MySQL Enterprise Monitor, were already part of Oracle's MySQL Enterprise 5.5 subscription version. And Oracle's new MySQL Enterprise extensions don't remove anything from the existing MySQL open-source code. But the new extensions cover areas that cut closer to core database functionality: scalability, high availability and security.

And according to Widenius, some of the functionality of the extensions rely on code that was contributed from outside Oracle. "The thread pool was originally developed by Ebay for MySQL 5.0 and contributed to MySQL to be include in MySQL 5.1," Widenius wrote on his blog. "The new pluggable authentication, which makes the new PAM authentication possible, was developed and contributed to Oracle by Sergei Golubchik at Monty Program Ab."

There are other pitfalls to the new extensions. The new MySQL Enterprise High Availability extension offers two options: Windows Server Failover Clustering, or virtual machine-based failover based on Oracle VM and Oracle Linux. Oracle doesn't support high-availability features on Red Hat Linux.

The outrage over Oracle's move isn't universal. Guissepe Maxia, former MySQL community manager, blogged in support of Oracle's move, saying that the commercial extensions would help pay the bills to fund further development of MySQL, and that he advocated giving paying customers features not available to the community while he was still at MySQL and subsequently at Sun. Part of the reason it hadn't been done earlier, he contended, was that MySQL AB lacked the quality assurance team internally to be able to release "reserved features" to subscription-holders, and had to depend on the community to test code.

But Oracle has also raised the bar for paid support in the process. In the last year, Oracle dropped the $599-a-year basic support option for commercial support, raising the entry level to $2000 a year per server for MySQL Standard edition. That, combined with concerns about the licensing requirements for the commercial software, may end up helping alternative support subscription providers like Percona and SkySQL.

"That's Oracle being Oracle, and there's nothing wrong with being Oracle," said Sandberg. "But it leaves a lot of customers unhappy. They really can't justify why you would raise the prices up drastically when you have the same product. That's how we get a lot of business." SkySQL, which is just reaching the end of its first fiscal year, has over 150 corporate customers signed up so far.