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Showing posts from February, 2018

Paper summary: Bitcoin-NG -- A scalable Blockchain Protocol

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This week in our seminar, we discussed the Bitcoin-NG paper. The paper appeared in NSDI 16, and is authored by Ittay Eyal, Adem Efe Gencer, Emin Gün Sirer, and Robbert van Renesse at the Cornell University.

The model section of this paper is very well formalized and written. This is like a Rosetta Stone find for classical distributed systems researchers that want to enter blockchain research. So in this summary, I will start by covering as much of that as I can.

The Nakamoto Consensus Problem  The blockchain system is comprised of a set of nodes N connected by a reliable peer-to-peer network. Nodes can generate public-private key-pairs for themselves. The system employs a cryptopuzzle system, defined by a cryptographic hash function H. The solution to a puzzle defined by the string y is a string x such that H(y|x) --the hash of the concatenation of the two-- is smaller than some target (i.e., the hash has k number of leading zeros). Each node i has a limited amount of compute power, c…

Paper review. IPFS: Content addressed, versioned, P2P file system

This week we discussed the IPFS whitepaper by Juan Benet in my Distributed Systems Seminar.

Remember peer-to-peer systems?IPFS is "peer-to-peer systems reloaded" with improved features. IPFS is a content-addressed distributed file system that combines Kademlia + BitTorrent + Git ideas. IPFS also offers better privacy/security features: it provides cryptographic hash content addressing, file integrity and versioning, and filesystem-level encryption and signing support.

The question is will it stick? I think it won't stick, but this work will still be very useful because we will transfer the best bits of IPFS to our datacenter computing as we did with other peer-to-peer systems technology. The reason I think it won't stick has nothing to do with the IPFS development/technology, but has everything to do with the advantages of centralized coordination and the problems surrounding decentralization. I rant more about this later in this post. Read on for the more detailed re…

Paper summary. SnailTrail: Generalizing critical paths for online analysis of distributed dataflows

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Monitoring is very important for distributed systems, and I wish it would receive more attention in research conferences. There has been work on monitoring for predicate detection purposes and for performance problem detection purposes. As machine learning and big data processing frameworks are seeing more action, we have been seeing more work on the latter category. For example in ML there have been work on how to figure out what is the best configuration to run. And in the context of general big data processing framework there has been work on identifying performance bottlenecks.

Collecting information and creating statistics about a framework to identify the bottleneck activities seems like an easy affair. However, the "making sense of performance" paper (2015) showed that this is not as simple as it seems, and sophisticated techniques such as blocked time analysis are needed to get a more accurate picture of performance bottlenecks.

This paper (by ETH Zurich and due to ap…

Think before you code

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I have been reading Flash boys by Michael Lewis. It is a fascinating book about Wall Street and high-frequency traders. I will write a review about the book later but I can't refrain from an overview comment. Apart from the greediness, malice, and sneakiness of Wall Street people, another thing that stood out about them was the pervasive cluelessness and ineptness. It turns out nobody knew what they were doing, including the people that are supposed to be regulating things, even sometimes the people that are gaming the system. This brought to my mind Steve Jobs' quote from his 1994 interview: "Everything in this world... was created by people no smarter than you."

Anyways, today I will talk about something completely different in the book that caught my eye. It is about thinking before coding.

On Page 132 of the book:
Russians had a reputation for being the best programmers on Wall Street, and Serge thought he knew why: They had been forced to learn to program comput…

Paper review. Blockchains from a distributed computing perspective

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Our distributed systems seminar met the first time this Monday. I went through the syllabus, explained how we will run the seminar, and introduced the papers we will discuss. In the second hour, to give students an overview of the blockchains technology, I went through this paper: "Blockchains from a distributed computing perspective".

I liked this paper a lot. It is from a respected distributed systems expert, Maurice Herlihy. It is written to be accessible and expository. The paper gives several examples (with increasing sophistication) to explain the blockchain concepts concretely. Finally, the paper is a perfect fit with our seminar's theme of looking at blockchains from a distributed systems perspective. Herlihy states that the paper is "colored by the perspective that much of the blockchain world is a disguised, sometimes distorted, mirror-image of the distributed computing world."

For a data processing perspective on blockchains, see this other paper.

Sim…

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