Past Meetup

PWL #15: The Dataflow Model and Millwheel: Fault tolerant stream processing

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Ankur Chauhan will present the latest research on stream processing systems that was recently presented at VLDB 2015 by the team at Google. The paper is titled: "The Dataflow Model: A Practical Approach to Balancing Correctness, Latency, and Cost in Massive-Scale, Unbounded, Out-of-Order Data Processing". This presents the state of the art in stream processing systems at scale and are also the technologies that lie at the heart of Google Cloud Dataflow (https://cloud.google.com/dataflow/what-is-google-cloud-dataflow).

Abstract:

Unbounded, unordered, global-scale datasets are increasingly common in day-to-day business (e.g. Web logs, mobile usage statistics, and sensor networks). At the same time, consumers of these datasets have evolved sophisticated requirements, such as event-time ordering and windowing by features of the data themselves, in addition to an insatiable hunger for faster answers. Meanwhile, practicality dictates that one can never fully optimize along all dimensions of correctness, latency, and cost for these types of input. As a result, data processing practitioners are left with the quandary of how to reconcile the tensions between these seemingly competing propositions, often resulting in disparate implementations and systems. We propose that a fundamental shift of approach is necessary to deal with these evolved requirements in modern data processing. We as a field must stop trying to groom unbounded datasets into finite pools of information that eventually become complete, and instead live and breathe under the assumption that we will never know if or when we have seen all of our data, only that new data will arrive, old data may be retracted, and the only way to make this problem tractable is via principled abstractions that allow the practitioner the choice of appropriate tradeoffs along the axes of interest: correctness, latency, and cost. In this paper, we present one such approach, the Dataflow Model, along with a detailed examination of the semantics it enables, an overview of the core principles that guided its design, and a validation of the model itself via the real-world experiences that led to its development.

Papers:

* The Dataflow Model: A Practical Approach to Balancing Correctness, Latency, and Cost in Massive-Scale, Unbounded, Out-of-Order Data Processing (http://www.vldb.org/pvldb/vol8/p1792-Akidau.pdf)

* MillWheel: Fault-Tolerant Stream Processing at Internet Scale (http://static.googleusercontent.com/media/research.google.com/en/us/pubs/archive/41378.pdf)