RE: Global snapshots

From: Andrey Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru>
> Thank you for this work!
> As I can see, main development difficulties placed in other areas: CSN, resolver,
> global deadlocks, 2PC commit... I'm not lawyer too. But if we get remarks from
> the patent holders, we can rewrite our Clock-SI implementation.

Yeah, I understand your feeling. I personally don't want like patents, and don't want to be disturbed by them. But the world is not friendly... We are not a lawyer, but we have to do our best to make sure PostgreSQL will be patent-free by checking the technologies as engineers.

Among the above items, CSN is the only concerning one. Other items are written in textbooks, well-known, and used in other DBMSs, so they should be free from patents. However, CSN is not (at least to me.) Have you checked if CSN is not related to some patent? Or is CSN or similar technology already widely used in famous software and we can regard it as patent-free?

And please wait. As below, the patent holder just says that Clock-SI is not based on the patent and an independent development. He doesn't say Clock-SI does not overlap with the patent or implementing Clock-SI does not infringe on the patent. Rather, he suggests that Clock-SI has many similarities and thus those may match the claims of the patent (unintentionally?) I felt this is a sign of risking infringement.

"The answer to your question is: No, Clock-SI is not based on the patent - it was an entirely independent development. The two approaches are similar in the sense that there is no global clock, the commit time of a distributed transaction is the same in every partition where it modified data, and a transaction gets it snapshot timestamp from a local clock. The difference is whether a distributed transaction gets its commit timestamp before or after the prepare phase in 2PC."

The timeline of events also worries me. It seems unnatural to consider that Clock-SI and the patent are independent.

2010/6 - 2010/9 One Clock-SI author worked for Microsoft Research as an research intern
2010/10 Microsoft filed the patent
2011/9 - 2011/12 The same Clock-SI author worked for Microsoft Research as an research intern
2013 The same author moved to EPFL and published the Clock-SI paper with another author who has worked for Microsoft Research since then.

So, could you give your opinion whether we can use Clock-SI without overlapping with the patent claims? I also will try to check and see, so that I can understand your technical analysis.

And I've just noticed that I got in touch with another author of Clock-SI via SNS, and sent an inquiry to him. I'll report again when I have a reply.

Regards
Takayuki Tsunakawa