Fundamental Oracle flaw revealed

Part of the problem is that you can't patch every system at once. Additionally, if you have a patched system with an elevated soft limit -- based on a multiplier of, say, 65,536 -- the SCN on that system could be higher than the SCN on an unpatched system using the original 16,384 multiplier, causing the unpatched system to refuse the connection or encounter another problem as it fails the soft limit check. There's also the issue of servers running older Oracle versions that may not have a patch available.

Furthermore, if this patch is a default inclusion in the next Oracle release, admins may suddenly discover that their existing servers are unable to communicate with new or upgraded servers that use the new, higher SCN calculation method, should the new servers have a sufficiently elevated SCN. If the SCN values line up just right, it's possible that a patched system could connect and set the SCN of an unpatched system just shy of the soft limit, causing the unpatched system to hit the limit through its own processing.

As mentioned, the risk of such a scenario playing out is very small except in large, highly interconnected environments where an elevated SCN can flow like a virus from server to server. But once a server is infected, there's no going back. Also, if the SCN is incremented arbitrarily -- or manually, with malicious intent -- then that 48-bit integer hard limit is suddenly not as astronomical as it might seem.

The community reactionInfoWorld contacted a number of Oracle sources for this story. Several lacked familiarity with the problem; others noted that Oracle licensing agreements prevented them from commenting on any aspect of their product usage. The head of the Independent Oracle User Group (IOUG), Andy Flower, offered this statement on the record: "This bug with the SCN number is obviously something our membership would be concerned about -- and will need to consider what sort of challenges that may present and if any mitigation strategies will be needed. I'm sure it will be a topic that some of our larger members will probably get together and discuss."

Among the Oracle experts we spoke with, Shirish Ojha, senior Oracle DBA for Logicworks, a hosting and private cloud service provider, was the most familiar with SCN issues, including the bug numbers associated with the problem. He acknowledges that although few Oracle environments are likely to encounter the problem, the consequences may be severe. "If there is a dramatic jump in SCN due to any Oracle bug, there is a minimalistic probability of breach of this seemingly high number," said Ojha, who has earned the coveted title of Oracle Certified Master. "If this occurs in a high-transaction and large interconnected Oracle architecture, this will render all interconnected Oracle databases useless in a short period of time."