RE: Global snapshots

Hi Andrey-san, all,

From: Andrey V. Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru>
> On 7/27/20 11:22 AM, tsunakawa(dot)takay(at)fujitsu(dot)com wrote:
> > Could you take a look at this patent? I'm afraid this is the Clock-SI for MVCC.
> Microsoft holds this until 2031. I couldn't find this with the keyword
> "Clock-SI.""
> >
> >
> > US8356007B2 - Distributed transaction management for database systems
> with multiversioning - Google Patents
> > https://patents.google.com/patent/US8356007
> >
> >
> > If it is, can we circumvent this patent?

> I haven't seen this patent before. This should be carefully studied.

I contacted 6 people individually, 3 holders of the patent and different 3 authors of the Clock-SI paper. I got replies from two people. (It's a regret I couldn't get a reply from the main author of Clock-SI paper.)

[Reply from the patent holder Per-Ake Larson]
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Thanks for your interest in my patent.

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.

Hope this helpful.

Best regards,
Per-Ake
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[Reply from the Clock-SI author Willy Zwaenepoel]
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Thank you for your kind words about our work.

I was unaware of this patent at the time I wrote the paper. The two came out more or less at the same time.

I am not a lawyer, so I cannot tell you if something based on Clock-SI would infringe on the Microsoft patent. The main distinction to me seems to be that Clock-SI is based on physical clocks, while the Microsoft patent talks about logical clocks, but again I am not a lawyer.

Best regards,

Willy.
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Does this make sense from your viewpoint, and can we think that we can use Clock-SI without infrindging on the patent? According to the patent holder, the difference between Clock-SI and the patent seems to be fewer than the similarities.

Regards
Takayuki Tsunakawa