Welcome!

SDN Journal Authors: Yeshim Deniz, Barbara Porter, Lori MacVittie, Elizabeth White, Jnan Dash

Related Topics: Java, SOA & WOA, .NET, Red Hat, Cloud Expo, SDN Journal

Java: Blog Feed Post

NoSQL and Partition Tolerance

While NoSQL implementations are aware that nodes have left, they are not aware that said nodes have formed a separate partition

I came across an article discussing NoSQL and partition tolerance.

The NoSQL Partition Tolerance Myth (link)

I may not entirely agree with the author.

But what most NoSQL systems offer is a peculiar behavior that is not partition tolerant, but partition oblivious instead.

 

No argument here. While NoSQL implementations are aware that nodes have left, they are not aware that said nodes have formed a separate partition.

In this case, we would want failure detection and carry out those transfers where the accounts are both on the same side of the partition, while denying or deferring transfers that cross the chasm.

The author is assuming that the account is only on one side of the partition. If that is that is case, is doesn’t matter whether the NoSQL implementation is eventually consistent or not. If the account is on both sides of the partition, the solution the author provides still results in an inconsistent state.

In such cases, it is almost always better to build services that degrade gracefully under partitions.

Bingo! The author implies that all NoSQL implementations sacrifice consistency in the event of a partition. That is not true. There are AP implementations (available & partition tolerant), and there are CP implementations (consistent & partition tolerant). However, an AP implementation can function as a CP implementation depending on the configuration and the application. For example, if accounts do not have multiple owners and the application can not withdraw funds from or deposit funds to an account if it can not access the account.

This post is not perfect and it is a bit outdated, but I think its helpful nonetheless.

Visual Guide to NoSQL Systems (link)

If I were to build a bank based on Dynamo, the granddaddy of all first-generation NoSQL data stores, it would silently split into two halves, like a lobotomized patient.

I would not say that Amazon Dynamo is the grandparent of all NoSQL implementations. I would say that there are two parents: Amazon Dynamo and Google BigTable. Then there are the grandparents…

A Brief History of NoSQL (link)

In this scenario, the hypothetical backend for Banko Dynamo would not only not provide any indication of failure, but allow a customer to create as many new accounts as there are partitions, one in each.

Why is the author now using account creation instead of withdrawals and deposits, and what is the relevance of creating multiple accounts? If my debit card does not work, I do not create a new account. That, and I maintain two checking accounts and one savings account with the same bank.

Let’s go back to withdrawals and deposits. If the accounts do not have multiple owners, it does not matter whether the NoSQL implementation is eventually consistent or not. If the accounts do have multiple owners, it depends on the NoSQL implementation. If it is inspired by Google BigTable (e.g. Apache HBase) or both Google BigTable and Amazon Dynamo (e.g. Apache Cassandra), it does not matter. These NoSQL implementations are CP, or can be configured to be CP. If it inspired only by Amazon Dynamo and it is eventually consistent, it may or may not matter…

Let’s assume that account withdrawals / deposits are separate from the accounts themselves and that the account is both consistent and available during a partition. The account has multiple owners but it is more or less read only.

My account has a balance of $100 (calculated from the withdrawals and deposits). Now, there are two partitions: A and B. I purchase $50 of St. Bernardus Abt 12 at Binny’s via partition A. Partition A now has withdrawal #1. I have dinner at Baume & Brix for $75 via partition B. Partition B now has withdrawal #2. My account has a balance of $50 in partition A. It has a balance of $25 in partition B. My account should have a balance of minus $25.

Does it matter? My account may not have a balance of minus $25, but it will. When the partition is repaired, the application will be able to access all of the withdrawals and deposits on my account. I may be charged an overlimit fee.

What if the NoSQL implementation sacrificed availability? My payment at Binny’s did not go through. That’s not a problem. No St. Bernardus Abt 12 for me. My payment at Baume & Brix did not go through. That’s a problem. I can’t pay for dinner. Baume & Brix can’t accept my payment nor that of any other customer paying with a debit card from the same bank as me via partition B.

What if I made a deposit of $25 at an ATM via partition A? My account will have a balance of $0 after the partition is repaired. I will not be charged an overlimit fee.

There are other scenarios. Perhaps I’m charged an insufficient funds fee and Baume & Brix does not receive payment. Perhaps Baume & Brix later resubmits the payment and receives payment.

Do you really want to sell tickets from both halves of your system? By definition, there is no way you can guarantee uniqueness of those tickets. There will be customers holding identical tickets with identical seat numbers.

Maybe, maybe not. If there is only a single owner per ticket, then yes. However, there may be availability issues. For example, partition A has tickets 1-150 and partition B has tickets 151-200. If all the tickets in partition B have been purchased, visitors may be unable to purchase tickets despite the fact that there may be tickets available in partition A. If there are multiple owners per ticket, I would prefer a NoSQL implementation that is CP. In this case, I would prefer to sacrifice availability rather than consistency.

Here is a better example. What if I report my debit card stolen? Sacrificing availability is not appropriate. What if customer service is accessing my account via the partition with no availability? My debit card must be reported stolen or the thief can continue to make purchases with it. Sacrificing consistency is not appropriate. The thief can continue to make purchases with my debit card via the partition where my account has not been reported stolen. Perhaps account information should not be stored in a distributed system.

And if they did, the first-generation NoSQL stores usually take the ultimate punt by presenting all versions of the divergent objects to the application, and let the application resolve the mess.

No argument here.

But if your data is that soft and inconsequential, why not just use memcached? It’s wicked fast, far faster than Mongo.

Perhaps because MongoDB is a document store and as such provides features that are not provided by key / value stores.

A lot of NoSQL developers pretend that being partition oblivious is a difficult thing to implement. This is false. It’s easy to make a program oblivious to a particular event; namely, you write no code to handle that event.

No argument here.

The thing that greatly helps first generation NoSQL data stores, the thing that enables them to package partition obliviousness as if it were equivalent to partition tolerance, is that they provide a very weak service guarantee in the first place. These systems cannot guarantee that, on a good day, your GET will return the latest PUT.

Sure they can.

In fact, eventual consistency means that a GET can return any previous value, including the Does Not Exist response from the very initial state of the system.

No argument here. Of course, not all NoSQL implementations are eventually consistent.


With all this being said, a NoSQL implementation may or may not be appropriate. To be more specific, a NoSQL implementation that is eventually consistent and sacrifices consistency in the event of a partition may or may not be appropriate. The behaviour is determined by the NoSQL implementation, its configuration, and the application that reads and writes to it. Whether that behaviour is appropriate or not depends on the business requirements.

Read the original blog entry...

More Stories By Daniel Thompson

I curate the content on this page, but the credit goes to my talented colleagues for the posts that you see here. Much of what you read on this page is the work of friends at How to JBoss, and I encourage you to drop by the site at http://www.howtojboss.com for some of the best JBoss technical and non-technical content for developers, architects and technology executives on the Web.

Cloud Expo Breaking News
Until recently, many organizations required specialized departments to perform mapping and geospatial analysis, and they used Esri on-premise solutions for that work. In his session at 15th Cloud Expo, Dave Peters, author of the Esri Press book Building a GIS, System Architecture Design Strategies for Managers, will discuss how Esri has successfully included the cloud as a fully integrated SaaS expansion of the ArcGIS mapping platform. Organizations that have incorporated Esri cloud-based applications and content within their business models are reaping huge benefits by directly leveraging cloud-based mapping and analysis capabilities within their existing enterprise investments. The ArcGIS mapping platform includes cloud-based content management and information resources to more widely, efficiently, and affordably deliver real-time actionable information and analysis capabilities to your organization.
In his session at 15th Cloud Expo, Mark Hinkle, Senior Director, Open Source Solutions at Citrix Systems Inc., will provide overview of the open source software that can be used to deploy and manage a cloud computing environment. He will include information on storage, networking(e.g., OpenDaylight) and compute virtualization (Xen, KVM, LXC) and the orchestration(Apache CloudStack, OpenStack) of the three to build their own cloud services. Speaker Bio: Mark Hinkle is the Senior Director, Open Source Solutions, at Citrix Systems Inc. He joined Citrix as a result of their July 2011 acquisition of Cloud.com where he was their Vice President of Community. He is currently responsible for Citrix open source efforts around the open source cloud computing platform, Apache CloudStack and the Xen Hypervisor. Previously he was the VP of Community at Zenoss Inc., a producer of the open source application, server, and network management software, where he grew the Zenoss Core project to over 10...
Almost everyone sees the potential of Internet of Things but how can businesses truly unlock that potential. The key will be in the ability to discover business insight in the midst of an ocean of Big Data generated from billions of embedded devices via Systems of Discover. Businesses will also need to ensure that they can sustain that insight by leveraging the cloud for global reach, scale and elasticity. In his session at Internet of @ThingsExpo, Mac Devine, Distinguished Engineer at IBM, will discuss bringing these three elements together via Systems of Discover.
As more applications and services move "to the cloud" (public or on-premise) cloud environments are increasingly adopting and building out traditional enterprise features. This in turn is enabling and encouraging cloud adoption from enterprise users. In many ways the definition is blurring as features like continuous operation, geo-distribution or on-demand capacity become the norm. NuoDB is involved in both building enterprise software and using enterprise cloud capabilities. In his session at 15th Cloud Expo, Seth Proctor, CTO at NuoDB, Inc., will discuss the experiences from building, deploying and using enterprise services and suggest some ways to approach moving enterprise applications into a cloud model.
Cloud and Big Data present unique dilemmas: embracing the benefits of these new technologies while maintaining the security of your organization’s assets. When an outside party owns, controls and manages your infrastructure and computational resources, how can you be assured that sensitive data remains private and secure? How do you best protect data in mixed use cloud and big data infrastructure sets? Can you still satisfy the full range of reporting, compliance and regulatory requirements? In his session at 15th Cloud Expo, Derek Tumulak, Vice President of Product Management at Vormetric, will discuss how to address data security in cloud and Big Data environments so that your organization isn’t next week’s data breach headline.
The cloud is everywhere and growing, and with it SaaS has become an accepted means for software delivery. SaaS is more than just a technology, it is a thriving business model estimated to be worth around $53 billion dollars by 2015, according to IDC. The question is – how do you build and scale a profitable SaaS business model? In his session at 15th Cloud Expo, Jason Cumberland, Vice President, SaaS Solutions at Dimension Data, will give the audience an understanding of common mistakes businesses make when transitioning to SaaS; how to avoid them; and how to build a profitable and scalable SaaS business.
SYS-CON Events announced today that Gridstore™, the leader in software-defined storage (SDS) purpose-built for Windows Servers and Hyper-V, will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Gridstore™ is the leader in software-defined storage purpose built for virtualization that is designed to accelerate applications in virtualized environments. Using its patented Server-Side Virtual Controller™ Technology (SVCT) to eliminate the I/O blender effect and accelerate applications Gridstore delivers vmOptimized™ Storage that self-optimizes to each application or VM across both virtual and physical environments. Leveraging a grid architecture, Gridstore delivers the first end-to-end storage QoS to ensure the most important App or VM performance is never compromised. The storage grid, that uses Gridstore’s performance optimized nodes or capacity optimized nodes, starts with as few a...
SYS-CON Events announced today that Solgenia, the global market leader in Cloud Collaboration and Cloud Infrastructure software solutions, will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Solgenia is the global market leader in Cloud Collaboration and Cloud Infrastructure software solutions. Designed to “Bridge the Gap” between personal and professional social, mobile and cloud user experiences, our solutions help large and medium-sized organizations dramatically improve productivity, reduce collaboration costs, and increase the overall enterprise value by bringing collaboration and infrastructure solutions to the cloud.
Cloud computing started a technology revolution; now DevOps is driving that revolution forward. By enabling new approaches to service delivery, cloud and DevOps together are delivering even greater speed, agility, and efficiency. No wonder leading innovators are adopting DevOps and cloud together! In his session at DevOps Summit, Andi Mann, Vice President of Strategic Solutions at CA Technologies, will explore the synergies in these two approaches, with practical tips, techniques, research data, war stories, case studies, and recommendations.
Enterprises require the performance, agility and on-demand access of the public cloud, and the management, security and compatibility of the private cloud. The solution? In his session at 15th Cloud Expo, Simone Brunozzi, VP and Chief Technologist(global role) for VMware, will explore how to unlock the power of the hybrid cloud and the steps to get there. He'll discuss the challenges that conventional approaches to both public and private cloud computing, and outline the tough decisions that must be made to accelerate the journey to the hybrid cloud. As part of the transition, an Infrastructure-as-a-Service model will enable enterprise IT to build services beyond their data center while owning what gets moved, when to move it, and for how long. IT can then move forward on what matters most to the organization that it supports – availability, agility and efficiency.
Every healthy ecosystem is diverse. This is especially true in cloud ecosystems, where portability and interoperability are more important than old enterprise models of proprietary ownership. In his session at 15th Cloud Expo, Mark Baker, Server Product Manager at Canonical/Ubuntu, will discuss how single vendors used to take the lead in creating and delivering technology, but in a cloud economy, where users want tools of their preference, when and where they need them, it makes no sense.
The 15th International Cloud Expo has just expanded its conference program, to bring together Cloud Computing, APM, APIs, Security, Big Data, Internet of Things, DevOps and WebRTC at one location. Cloud Expo is the single show where delegates and technology vendors can meet to experience and discuss the entire world of the cloud. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to learn about the latest technology developments and solutions.
SYS-CON Events announced today that Bsquare Corporation, a leading enabler of smart connected systems, has been named “Bronze Sponsor” of SYS-CON's Internet of @ThingsExpo, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Bsquare is a global leader of embedded software solutions. We enable smart connected systems at the device level and beyond that millions use every day and provide actionable data solutions for the growing Internet of Things (IoT) market. We empower our world-class customers with our products, services and solutions to achieve innovation and success.
SYS-CON Events announced today that NuoDB, Inc., the leader in webscale distributed database technology, has been named “Bronze Sponsor” of SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. NuoDB was launched in 2010 by industry-renowned database architect Jim Starkey and accomplished software CEO Barry Morris to deliver a webscale distributed database management system that is specifically designed for the cloud and the modern datacenter.
SYS-CON Events announced today that Cloudian, Inc., the leading provider of hybrid cloud storage solutions, has been named “Bronze Sponsor” of SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Cloudian is a Foster City, Calif.-based software company specializing in cloud storage. Cloudian HyperStore® is an S3-compatible cloud object storage platform that enables service providers and enterprises to build reliable, affordable and scalable hybrid cloud storage solutions. Cloudian actively partners with leading cloud computing environments including Amazon Web Services, Citrix Cloud Platform, Apache CloudStack, OpenStack and the vast ecosystem of S3 compatible tools and applications. Cloudian's customers include Vodafone, Nextel, NTT, Nifty, and LunaCloud. The company has additional offices in China and Japan.