The Scalability Dilemma and the Case for Decoupling

By Justin Y. Shi, Temple University

March 30, 2016

The need for extreme scale computing is driven by the seemingly forever fledgling Internet. In abstract, the entire network is already an extreme scale computing engine. The technical difficulty, however, is to harness the dispersed computing powers for a single purpose. An analogy to this would be to build an engine capable of harnessing the combustive power of elements to move people or things. The presence of such an engine could drive transformative changes in technology, society and the economy.

The first requirement for such an extreme scale computing engine is the ability to gain incrementally better performance and reliability while concurrently expanding in size. We expect more from this engine than we do from a sports car. The “cost of doing business” should only include oil changes, tire and bearing replacements, but not re-building the car when a tire bursts or the engine upgrades. Unlike sports cars, technically, the extreme scale computing engine should run faster and more reliably when it expands for solving a bigger problem. While the top deliverable performance of the engine must be capped by the aggregate of available capabilities, there should be no loss in an application’s reliability when expanding in size.

Reliable distributed computing is hard. A 1993 paper entitled “The Impossibility of Implementing Reliable Communication in the Face of Crashes”[i] drew a “line in the sand.” It was proved that given a pair of sender and receiver, reliable communication between them is impossible if either one or the other could crash arbitrarily. It follows immediately that any distributed or parallel application that depends on fixed program-processor bindings must face the increased risk of crashes when the application expands, namely the “scalability dilemma.”

ImpossibilityProof 800xThe corollary of the impossibility proof is that reliable failure detection is also impossible. Thus, fault detection/repair/reschedule schemes are technically flawed for extreme scale computing. In this context, “reliability” means “100% application reliability while the system affords greater than the minimal survivable resource set.” For any computing or communication application, the “minimal survivable resource set” includes “at least one viable resource at every critical path at the time of need.”

Ironically, the possibility of such a highly reliable system using faulty networks was also proved by the same authors[ii]. Today’s Internet is a feasibility study of the correctness of this proof. These two complementary studies somehow seem contradictory to most people. This confusion may be rooted in a widespread faulty assumption in distributed computing communities: the “virtual circuit.” It is widely taught and believed that a virtual circuit is “a reliable, lossless data transmission channel between two communicating programs.” Historically, this term was first created by the network communities to signify a clean “hand-off point” for computing communities. The trouble was that the computing professionals took the liberty to expand the virtual circuit definition to include the reliability of the communicating programs.

This was an unfortunate mistake. It crossed the “line in the sand.” This problem was quickly identified as the first fallacy – “the network is reliable” — in the “Eight Fallacies of Distributed Computing”[iii]. However, in the last three decades, the industry and research communities have continued to ignore the warning signs despite increasing service downtimes and data losses in today’s large scale distributed systems (including all mission critical applications and HPC applications).

The Stateless Parallel Processing (“SPP”) concept [iv]was conceived in the mid-1980s based on a practical requirement of a mission critical project called “Zodiac.” The requirement was very basic: Keep a distributed application running regardless partial component failures. It was inconceivable for national security to rely on any mission critical application that could crash on a single component failure. Technically speaking, mission critical programs and data must be completely decoupled from processing, communication and storage devices. Otherwise, any device failure can halt the entire application and expanding the processing infrastructure will inevitably result in a higher probability of service interruptions, data losses, and runaway maintenance costs. HPC applications are the first non-lethal applications to demonstrate these potentially disastrous consequences. The growing instabilities in large scale simulations have also already played a role in the investigation of the scientific computing reproducibility problems[v].

Methods for building completely decoupled applications are fundamentally different from those for “bare metal” applications. The first difference is in the design of Application Programming Interface (“API”). Technically, Remote Procedure Call (“RPC”), Message Passing Interface (“MPI”), share memory (“OpenMP”), and Remote Method Invocation (“RMI”) are all “bare metal”-inspired APIs. Applications built using these APIs force the runtime systems to generate fixed program-processor dependencies. They have crossed the “line in the sand.” The computing application scalability dilemma is unavoidable.

The <key, value=””>-based APIs, such as Hadoop, Spark, and Scality, aimed to relax the program/data-device dependency by allowing the runtime system to conduct failure detection/repair “magic.” These efforts have already shown significant scalability gains against “bare metal” approaches. Unfortunately, due to the influence of the “virtual circuit” concept, their runtime implementations have also crossed the “line in the sand.” The natural next step is to completely decouple devices from programs and data.

As the “Internet of Things” takes afoot, the “smart big sensing” challenge is on the horizon. In this context, an extreme scale computing engine is merely a necessity for survival. The existing distributed and parallel computing technologies are woefully inadequate.

Fundamentally, all electronics will fail in unexpected ways. “Bare metal” computing was important decades ago but detrimental to large scale computing. It is simply flawed for extreme scale computing.

Albert Einstein defined “Insanity” as doing “the same thing over and over again and expecting a different result”. Without a paradigm shift, we can continue to call anything “extreme scale” while secretly keeping the true extreme scale engine in our dreams.


[i] Alan Fekete, Nancy A. Lynch, Yishay Mansour, John Spinelli, “The Impossibility of Implementing Reliable Communication in the Face of Crashes,” Journal of the ACM, 1993.

[ii] John Spinelli, “Reliable Data Communication in Faulty Computer Networks.” Ph.D. dissertation. Dept. Elect. Eng. Comput. Sci., Massachusetts Institute of Technology, Cambridge, Mass., and MIT Laboratory for Information and Decision Systems report LIDS-TH-1882, June 1984.

[iii] Peter Deutsch, “Eight Fallacies of Distributed Computing,”

[iv] Justin Shi, “Stateless Parallel Processing Prototype: Synergy”.

[v] XSEDE 2014 Reproducibility Workshop Report, “Standing Together for Reproducibility in Large-Scale Computing”.

Subscribe to HPCwire's Weekly Update!

Be the most informed person in the room! Stay ahead of the tech trends with industy updates delivered to you every week!

IBM Research Scales to 11,400 Cores for EDA

August 5, 2021

For many HPC users, their needs are not evenly distributed throughout a year: some might need few – if any – resources for months, then they might need a very large system for a week. For those kinds of users, large Read more…

Careers in Cybersecurity Featured at PEARC21

August 5, 2021

The PEARC21 (Practice & Experience in Advanced Research Computing) Student Program featured a Cybersecurity Careers Panel. Five experts shared lessons learned from more than 100 years of combined experience. While it Read more…

HPC Career Notes: August 2021 Edition

August 4, 2021

In this monthly feature, we’ll keep you up-to-date on the latest career developments for individuals in the high-performance computing community. Whether it’s a promotion, new company hire, or even an accolade, we’ Read more…

The Promise (and Necessity) of Runtime Systems like Charm++ in Exascale Power Management

August 4, 2021

Big heterogeneous computer systems, especially forthcoming exascale computers, are power hungry and difficult to program effectively. This is, of course, not an unrecognized problem. In a recent blog, Charmworks’ CEO S Read more…

Digging into the Atos-Nimbix Deal: Big US HPC and Global Cloud Aspirations. Look out HPE?

August 2, 2021

Behind Atos’s deal announced last week to acquire HPC-cloud specialist Nimbix are ramped-up plans to penetrate the U.S. HPC market and global expansion of its HPC cloud capabilities. Nimbix will become “an Atos HPC c Read more…

AWS Solution Channel

Pushing pixels, not data with NICE DCV

NICE DCV, our high-performance, low-latency remote-display protocol, was originally created for scientists and engineers who ran large workloads on far-away supercomputers, but needed to visualize data without moving it. Read more…

Berkeley Lab Makes Strides in Autonomous Discovery to Tackle the Data Deluge

August 2, 2021

Data production is outpacing the human capacity to process said data. Whether a giant radio telescope, a new particle accelerator or lidar data from autonomous cars, the sheer scale of the data generated is increasingly Read more…

Careers in Cybersecurity Featured at PEARC21

August 5, 2021

The PEARC21 (Practice & Experience in Advanced Research Computing) Student Program featured a Cybersecurity Careers Panel. Five experts shared lessons learn Read more…

Digging into the Atos-Nimbix Deal: Big US HPC and Global Cloud Aspirations. Look out HPE?

August 2, 2021

Behind Atos’s deal announced last week to acquire HPC-cloud specialist Nimbix are ramped-up plans to penetrate the U.S. HPC market and global expansion of its Read more…

What’s After Exascale? The Internet of Workflows Says HPE’s Nicolas Dubé

July 29, 2021

With the race to exascale computing in its final leg, it’s natural to wonder what the Post Exascale Era will look like. Nicolas Dubé, VP and chief technologist for HPE’s HPC business unit, agrees and shared his vision at Supercomputing Frontiers Europe 2021 held last week. The next big thing, he told the virtual audience at SFE21, is something that will connect HPC and (broadly) all of IT – into what Dubé calls The Internet of Workflows. Read more…

How UK Scientists Developed Transformative, HPC-Powered Coronavirus Sequencing System

July 29, 2021

In November 2020, the COVID-19 Genomics UK Consortium (COG-UK) won the HPCwire Readers’ Choice Award for Best HPC Collaboration for its CLIMB-COVID sequencing project. Launched in March 2020, CLIMB-COVID has now resulted in the sequencing of over 675,000 coronavirus genomes – an increasingly critical task as variants like Delta threaten the tenuous prospect of a return to normalcy in much of the world. Read more…

IBM and University of Tokyo Roll Out Quantum System One in Japan

July 27, 2021

IBM and the University of Tokyo today unveiled an IBM Quantum System One as part of the IBM-Japan quantum program announced in 2019. The system is the second IB Read more…

Intel Unveils New Node Names; Sapphire Rapids Is Now an ‘Intel 7’ CPU

July 27, 2021

What's a preeminent chip company to do when its process node technology lags the competition by (roughly) one generation, but outmoded naming conventions make it seem like it's two nodes behind? For Intel, the response was to change how it refers to its nodes with the aim of better reflecting its positioning within the leadership semiconductor manufacturing space. Intel revealed its new node nomenclature, and... Read more…

Will Approximation Drive Post-Moore’s Law HPC Gains?

July 26, 2021

“Hardware-based improvements are going to get more and more difficult,” said Neil Thompson, an innovation scholar at MIT’s Computer Science and Artificial Intelligence Lab (CSAIL). “I think that’s something that this crowd will probably, actually, be already familiar with.” Thompson, speaking... Read more…

With New Owner and New Roadmap, an Independent Omni-Path Is Staging a Comeback

July 23, 2021

Put on a shelf by Intel in 2019, Omni-Path faced a uncertain future, but under new custodian Cornelis Networks, OmniPath is looking to make a comeback as an independent high-performance interconnect solution. A "significant refresh" – called Omni-Path Express – is coming later this year according to the company. Cornelis Networks formed last September as a spinout of Intel's Omni-Path division. Read more…

AMD Chipmaker TSMC to Use AMD Chips for Chipmaking

May 8, 2021

TSMC has tapped AMD to support its major manufacturing and R&D workloads. AMD will provide its Epyc Rome 7702P CPUs – with 64 cores operating at a base cl Read more…

Berkeley Lab Debuts Perlmutter, World’s Fastest AI Supercomputer

May 27, 2021

A ribbon-cutting ceremony held virtually at Berkeley Lab's National Energy Research Scientific Computing Center (NERSC) today marked the official launch of Perlmutter – aka NERSC-9 – the GPU-accelerated supercomputer built by HPE in partnership with Nvidia and AMD. Read more…

Ahead of ‘Dojo,’ Tesla Reveals Its Massive Precursor Supercomputer

June 22, 2021

In spring 2019, Tesla made cryptic reference to a project called Dojo, a “super-powerful training computer” for video data processing. Then, in summer 2020, Tesla CEO Elon Musk tweeted: “Tesla is developing a [neural network] training computer called Dojo to process truly vast amounts of video data. It’s a beast! … A truly useful exaflop at de facto FP32.” Read more…

Google Launches TPU v4 AI Chips

May 20, 2021

Google CEO Sundar Pichai spoke for only one minute and 42 seconds about the company’s latest TPU v4 Tensor Processing Units during his keynote at the Google I Read more…

CentOS Replacement Rocky Linux Is Now in GA and Under Independent Control

June 21, 2021

The Rocky Enterprise Software Foundation (RESF) is announcing the general availability of Rocky Linux, release 8.4, designed as a drop-in replacement for the soon-to-be discontinued CentOS. The GA release is launching six-and-a-half months after Red Hat deprecated its support for the widely popular, free CentOS server operating system. The Rocky Linux development effort... Read more…

Intel Launches 10nm ‘Ice Lake’ Datacenter CPU with Up to 40 Cores

April 6, 2021

The wait is over. Today Intel officially launched its 10nm datacenter CPU, the third-generation Intel Xeon Scalable processor, codenamed Ice Lake. With up to 40 Read more…

Iran Gains HPC Capabilities with Launch of ‘Simorgh’ Supercomputer

May 18, 2021

Iran is said to be developing domestic supercomputing technology to advance the processing of scientific, economic, political and military data, and to strengthen the nation’s position in the age of AI and big data. On Sunday, Iran unveiled the Simorgh supercomputer, which will deliver.... Read more…

10nm, 7nm, 5nm…. Should the Chip Nanometer Metric Be Replaced?

June 1, 2020

The biggest cool factor in server chips is the nanometer. AMD beating Intel to a CPU built on a 7nm process node* – with 5nm and 3nm on the way – has been i Read more…

Leading Solution Providers


Julia Update: Adoption Keeps Climbing; Is It a Python Challenger?

January 13, 2021

The rapid adoption of Julia, the open source, high level programing language with roots at MIT, shows no sign of slowing according to data from I Read more…

AMD-Xilinx Deal Gains UK, EU Approvals — China’s Decision Still Pending

July 1, 2021

AMD’s planned acquisition of FPGA maker Xilinx is now in the hands of Chinese regulators after needed antitrust approvals for the $35 billion deal were receiv Read more…

GTC21: Nvidia Launches cuQuantum; Dips a Toe in Quantum Computing

April 13, 2021

Yesterday Nvidia officially dipped a toe into quantum computing with the launch of cuQuantum SDK, a development platform for simulating quantum circuits on GPU-accelerated systems. As Nvidia CEO Jensen Huang emphasized in his keynote, Nvidia doesn’t plan to build... Read more…

Microsoft to Provide World’s Most Powerful Weather & Climate Supercomputer for UK’s Met Office

April 22, 2021

More than 14 months ago, the UK government announced plans to invest £1.2 billion ($1.56 billion) into weather and climate supercomputing, including procuremen Read more…

Quantum Roundup: IBM, Rigetti, Phasecraft, Oxford QC, China, and More

July 13, 2021

IBM yesterday announced a proof for a quantum ML algorithm. A week ago, it unveiled a new topology for its quantum processors. Last Friday, the Technical Univer Read more…

Q&A with Jim Keller, CTO of Tenstorrent, and an HPCwire Person to Watch in 2021

April 22, 2021

As part of our HPCwire Person to Watch series, we are happy to present our interview with Jim Keller, president and chief technology officer of Tenstorrent. One of the top chip architects of our time, Keller has had an impactful career. Read more…

Frontier to Meet 20MW Exascale Power Target Set by DARPA in 2008

July 14, 2021

After more than a decade of planning, the United States’ first exascale computer, Frontier, is set to arrive at Oak Ridge National Laboratory (ORNL) later this year. Crossing this “1,000x” horizon required overcoming four major challenges: power demand, reliability, extreme parallelism and data movement. Read more…

Senate Debate on Bill to Remake NSF – the Endless Frontier Act – Begins

May 18, 2021

The U.S. Senate today opened floor debate on the Endless Frontier Act which seeks to remake and expand the National Science Foundation by creating a technology Read more…

  • arrow
  • Click Here for More Headlines
  • arrow