Mothy's talk is happening now!

On Sun, Apr 8, 2018 at 5:03 PM, Tom Anderson <> wrote:

> Revised, now with Ihsan's schedule and abstract.
> ----
> With NSDI being local, we have a number of talks queued up this week, and
> most of the visitors will have time after/before to meet with us.  Please
> sign up!   Note that several of the talks have non-standard start times.
> Abstracts collected below.
> Wednesday, CSE 305, 1:30pm
> Vijay Chidambaram, UT Austin
> PebblesDB: Building Key-Value Stores Using Fragmented Log-Structured Merge
> Trees
> &month=04&day=11&room=3050&area=5
> Thursday, CSE 305, 11am
> Mothy Roscoe, ETH Zurich
> Enzian: Research Computer
> &month=4&day=8&area=5&room=3080
> Thursday, CSE 305, 12pm
> Ihsan Qazi, LUMS
> Understanding Internet Access in the Developing World
> &month=04&day=12&area=5&room=3113
> Friday, CSE 305, 12:00pm
> Keith Winstein, Stanford
> Tiny Functions for Codecs, Compilation, and (maybe) Everything
> &month=4&day=8&area=5&room=3103
> ----
> PebblesDB: Building Key-Value Stores Using Fragmented Log-Structured Merge
> Trees
> Key-value stores such as LevelDB and RocksDB have become a fundamental
> part of the systems infrastructure. However, these stores suffer from high
> write amplification: for example, 45 GB of data written to RocksDB results
> in 1.8 TB (28x) written to storage. In this talk, I show that the write
> amplification problem is fundamental to the Log-Structured Merge Trees data
> structure that underlies these stores. I present a novel data structure
> that is inspired by Skip Lists, termed Fragmented Log-Structured Merge
> Trees (FLSM). FLSM introduces the notion of guards to organize logs, and
> avoids rewriting data in the same level. I will describe PebblesDB, a new
> key-value store that we built by modifying HyperLevelDB to use the FLSM
> data structure. I will briefly present our evaluation which shows that
> PebblesDB increases write throughput by 6.7x (compared to RocksDB and
> LevelDB) while simultaneously reducing write amplification by 2.4-3x.
> PebblesDB is open-source (, and I
> hope to convince some of you to incorporate it into new systems you build :)
> Enzian: Research Computer
> Academic research in rack-scale and datacenter computing
> today is hamstrung by lack of hardware.  Cloud providers and hardware
> vendors build custom accelerators, interconnects, and networks for
> commercially important workloads, but university researchers are stuck
> with commodity, off-the-shelf parts.
> Enzian is a research computer developed at ETH Zurich in collaboration
> with Cavium and Xilinx which addresses this problem.  An Enzian board
> consists of a server-class ARMv8 SoC tightly coupled and coherent with
> a large FPGA (eliminating PCIe), with about 0.5 TB DDR4 and about 600
> Gb/s of network I/O either to the CPU (over Ethernet) or directly to
> the FPGA (potentially over custom protocols).  Enzian runs both
> Barrelfish and Linux operating systems.
> Many Enzian boards can be connected in a rack-scale machine (either
> with or without a discrete switch), and the design is intended to
> allow many different research use-cases: zero-overhead run-time
> verification of software invariants, novel interconnect protocols for
> remote memory access, hardware enforcement of access control in a
> large machine, high-performance streaming analytics using a
> combination of software and configurable hardware, and much more.
> By providing a powerful and flexible platform for computer systems
> research, Enzian aims to enable more relevant and far-reaching work on
> future compute platforms.
> Understanding Internet Access in the Developing World
> In this talk, I will present my recent research on Internet access in
> developing countries. In the first half of my talk, I will present a study
> on the characteristics of mobile devices in developing regions. Using a
> dataset of 0.5 million subscribers from one of the largest cellular
> operators in Pakistan, I will present an analysis of cell phones being used
> based on different features (e.g., CPU, memory, and cellular interface).
> Our analysis reveals potential device-level bottlenecks for Internet
> access, which can inform infrastructure design for improving mobile web
> performance. (This work appeared in ACM IMC 2016) Another accessibility
> challenge in developing countries is the rise in Internet censorship
> events, which can have a substantial impact on various stakeholders in the
> Internet ecosystem (e.g., users, content providers, ISPs, and advertisers).
> In the second half of my talk, I will discuss how Internet censorship poses
> an economic threat to online advertising, which plays an essential role in
> enabling the free Web by allowing publishers to monetize their services.
> Then I will describe a system we designed that enables relevant ads while
> retaining the effectiveness of censorship resistance tools (e.g., Tor).
> (This work appeared in ACM HotNets 2017)
> Tiny Functions for Codes, Compilation, and (maybe) Soon Everything
> Networks, applications, and media codecs frequently treat one another as
> strangers. By expressing large systems as compositions of small, pure
> functions, we've found it's possible to achieve tighter couplings between
> these components, improving performance without giving up modularity or the
> ability to debug. I'll discuss our experience with systems that demonstrate
> this basic idea: ExCamera (NSDI 2017) parallelizes video encoding into
> thousands of tiny tasks, each handling a fraction of a second of video,
> much shorter than the interval between key frames, and executing in
> parallel on AWS Lambda. This was the first system to demonstrate
> "burst-parallel" thousands-way computation on functions-as-a-service
> infrastructure. Salsify (NSDI 2018) is a low-latency network video system
> that uses a purely functional video codec to explore execution paths of the
> encoder without committing to them, allowing it to closely match the
> capacity estimates from a video-aware transport protocol. This architecture
> outperforms more loosely-coupled applications -- Skype, Facetime, Hangouts,
> WebRTC -- in delay and visual quality, and suggests that while improvements
> in video codecs may have reached the point of diminishing returns, video
> systems still have low-hanging fruit. Lepton (NSDI 2017) uses a purely
> functional JPEG/VP8 transcoder to compress images in parallel across a
> distributed network filesystem with arbitrary block boundaries. This
> free-software system is in production at Dropbox and has compressed, by
> 23%, more than 200 petabytes of user JPEGs.
> Based on our experience, we propose an intermediate representation for
> interactive lambda computing, called cloud "thunks" -- stateless closures
> that describe their data-dependencies by content-hash, separating the
> specification of an algorithm from its schedule and execution. We have
> created a tool that extracts this IR from off-the-shelf software build
> systems, letting the user treat a FaaS service like a 5,000-core build farm
> with global memoization of results. Expressing systems and protocols as
> compositions of small, pure functions has the potential to lead to a wave
> of "general-purpose" lambda computing, permitting us to transform everyday
> time-consuming operations into large numbers of functions executing with
> massive parallelism for short durations in the cloud.
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