
A Critique of ANSI SQL Isolation Levels (1995) [pdf] - luu
https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/tr-95-51.pdf
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mjb
This is a classic paper, and well worth reading if you use relational
databases for anything serious. Using 'phenomena' is a nice framing, and one
that I found particularly effective for understanding how to write correct
database transactions at various isolation levels. Perhaps the most surprising
result here is "REPEATABLE READ »« Snapshot Isolation", meaning that it's not
possible to order one of the two as "stronger" isolation.

The author list here is a round-up of real database legends, including the
late Jim Gray and Pat O'Neil, and Phil Bernstein and Elizabeth O'Neil who are
still doing work in databases and systems.

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DenisM
Also, to your point, I believe it is possible to strengthen Snapshot Isolation
to the point where it is strictly stronger than Repeatable Read. There was a
paper at VLDB circa 2007, I belie it was done by a researcher from Oracle.
Can't recall any details, other than the guy was pretty young and well-spoken.

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petergeoghegan
I believe that you're thinking of Michael J. Cahill:

[https://courses.cs.washington.edu/courses/cse444/08au/544M/R...](https://courses.cs.washington.edu/courses/cse444/08au/544M/READING-
LIST/fekete-sigmod2008.pdf)

This became the basis of PostgreSQL's serializable snapshot isolation feature:

[https://drkp.net/papers/ssi-vldb12.pdf](https://drkp.net/papers/ssi-
vldb12.pdf)

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DenisM
Quite possible. In the years since my brain has completely unloaded
transaction processing to make room for supply chain management, so I can no
longer relate to the subject to see if it's the same research. :(

I recall I approached him in the break and congratulated him on the fantastic
presentation. And it was fantastic - like a murder mystery story, it kept you
on the edge of the seat, answering questions it has created earlier and
culminating into _the_ answer. An older guy, probably his science advisor,
protested that it's not only the presentation that was good, and the research
itself was not too shabby. To that I retorted that for all we know there was a
lot of good research in the room but we will never find out because delivery
was lacking. Research must beget research, it's what makes science from hobby.
I think we reached an agreement. I often think back to that moment - what we
build should lend itself to further building, or it becomes a dead end.
Neither science nor technology are made from dead-ends, the proverbial
shoulders of giants must stack up for the civilization to advance.

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petergeoghegan
Here is the thesis itself:

[https://ses.library.usyd.edu.au/bitstream/handle/2123/5353/m...](https://ses.library.usyd.edu.au/bitstream/handle/2123/5353/michael-
cahill-2009-thesis.pdf)

I do remember thinking that it was unusually well argued and presented. It's
much more accessible to the practitioner than a lot of the other research in
this area. In my experience this is a positive signal about the quality of the
research.

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DenisM
That's gotta be him. I just read the abstract, it's mountain-creek-clear.

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hypewatch
If anyone would like to learn more about this topic, Jepsen has some great
articles on isolation levels and consistency models.

[https://jepsen.io/consistency](https://jepsen.io/consistency)

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andrewxdiamond
(1995)

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dang
Added. Thanks!

