Pat Helland

Building distributed systems & databases since 1978. Now at Salesforce. Dropped out of UC Irvine in 1976. Write for ACM Queue & blog @

[Pat Helland @PatHelland]

@reubenbond @jorandirkgreef @jangray It will be great to get to know you! I'm looking forward to HPTS. Since it runs every two years, it's only my 20th time attending. :-)

[Pat Helland @PatHelland]

@jorandirkgreef @jangray Yeah... Some things never change.
When it comes to me talking all the time,
I'm IM-MUTE-ABLE.

[Pat Helland @PatHelland]

@jorandirkgreef @jangray I'm looking forward to talking to you @jorandirkgreef about this at HPTS! Thank you for your kind words.
Warm regards
Pat

[Pat Helland @PatHelland]

@MarcJBrooker In high school, my nickname was "A-tella the Pun".

[Pat Helland @PatHelland]

@LewisCTech Thank you for your kindness, @LewisCTech !

Indeed, an essential form of interaction across systems is what happens across trust boundaries. I started talking about that in 1999 even before SOA came along or the CIDR 2005 paper happened.

See: https://t.co/QCvA0T1aDf for more.

[Pat Helland @PatHelland]

@MarcJBrooker Snapshot seems to be the practical choice. There may be something to be said for natural selection.

It’s the most commonly used isolation model. I certainly didn’t anticipate that. Go figure…

[Pat Helland @PatHelland]

@nevgeniev @sunbains @jorandirkgreef @conor_power23 Atomic units (on IBM mainframes) were LUW (Logical Unit of Work).

Business operations (sometimes spanning weeks) are bigger concepts.

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[Pat Helland @PatHelland]

@nevgeniev @sunbains @jorandirkgreef @conor_power23 The word "transaction" has a convoluted history. In the 1970s, it pretty much meant a human interaction with an online system. These were not too common at the time and mostly used for high-end complex systems like airline reservations.

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[Pat Helland @PatHelland]

@sunbains @jorandirkgreef @conor_power23 Coping with longer times and distributed space is very interesting and challenging. Building based on classic transactions is a simplifying piece of the puzzle.

There are still challenges, though!

Lots of fun issues.

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[Pat Helland @PatHelland]

@sunbains @jorandirkgreef @conor_power23 Yeah... But all joking aside, classic DB transactions routinely end up being the building blocks underlying long running sagas, workflows, and more.

Transactions "normally" apply to a single point in time (the commit time in the DB) and a single point in space (the DB).

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[Pat Helland @PatHelland]

@halberenson @MarcJBrooker @Hippotas Naahh... You've been both tired and re-tired.
You know LOTS about the subject... Be careful before you weigh in. It might be interesting to you.

Danger!

[Pat Helland @PatHelland]

@reubenbond @MarcJBrooker Discussions of the tradeoffs between isolation levels and their importance to the app are interesting. Still, that's not the goal of my BIG DEAL paper.

I picked one and tried to explore the asymptotic limits to scale.

These debates are separate (and fun). :-)
/end

[Pat Helland @PatHelland]

@reubenbond @MarcJBrooker Isolation levels are COMPLEX for the application. Strengthen them and an existing app may break.
Weaken them and an existing app may break.

My "BIG DEAL" paper picked one and explored issues of asymptotic limits to scale. That was the goal!

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[Pat Helland @PatHelland]

@MarcJBrooker Yup.

Of course, I acknowledge that.

Still, VAST numbers of apps use snapshot isolation for one (or both) of two reasons:
- It's what they have available,
- It scales better than serializability.

My argument is that this IS what happens, not a judgement of goodness.

[Pat Helland @PatHelland]

@MarcJBrooker Provoking discussion and debate (as well as new ideas) was my goal for the paper. Thank you for contributing to the discussion.

As alway, "hat tip" to my friend!

- Pat
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[Pat Helland @PatHelland]

@MarcJBrooker I would add is that a HUGE number of existing apps (perhaps more than half) use some variant of snapshot isolation.

The BIG DEAL paper is about OLTP scale for OLTP, app implementation challenges. ARGUABLY, the value of scale for the dominant isolation is most important.

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