|By Daniel Thompson||
|March 14, 2013 12:00 PM EDT||
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This post is not perfect and it is a bit outdated, but I think its helpful nonetheless.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.
DevOps tends to focus on the relationship between Dev and Ops, putting an emphasis on the ops and application infrastructure. But that’s changing with microservices architectures. In her session at DevOps Summit, Lori MacVittie, Evangelist for F5 Networks, will focus on how microservices are changing the underlying architectures needed to scale, secure and deliver applications based on highly distributed (micro) services and why that means an expansion into “the network” for DevOps.
Jul. 1, 2015 07:15 PM EDT Reads: 2,534
"We have a tagline - "Power in the API Economy." What that means is everything that is built in applications and connected applications is done through APIs," explained Roberto Medrano, Executive Vice President at Akana, in this SYS-CON.tv interview at 16th Cloud Expo, held June 9-11, 2015, at the Javits Center in New York City.
Jul. 1, 2015 05:00 PM EDT Reads: 893
Containers have changed the mind of IT in DevOps. They enable developers to work with dev, test, stage and production environments identically. Containers provide the right abstraction for microservices and many cloud platforms have integrated them into deployment pipelines. DevOps and Containers together help companies to achieve their business goals faster and more effectively. In his session at DevOps Summit, Ruslan Synytsky, CEO and Co-founder of Jelastic, reviewed the current landscape of...
Jul. 1, 2015 05:00 PM EDT Reads: 2,233
"AgilData is the next generation of dbShards. It just adds a whole bunch more functionality to improve the developer experience," noted Dan Lynn, CEO of AgilData, in this SYS-CON.tv interview at 16th Cloud Expo, held June 9-11, 2015, at the Javits Center in New York City.
Jul. 1, 2015 04:09 PM EDT Reads: 650
The Internet of Things is not only adding billions of sensors and billions of terabytes to the Internet. It is also forcing a fundamental change in the way we envision Information Technology. For the first time, more data is being created by devices at the edge of the Internet rather than from centralized systems. What does this mean for today's IT professional? In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists addressed this very serious issue of pro...
Jul. 1, 2015 03:30 PM EDT Reads: 1,087
"We provide a web application framework for building really sophisticated web applications that run on a browser without any installation need so we get used for biotech, defense, and banking applications," noted Charles Kendrick, CTO and Chief Architect at Isomorphic Software, in this SYS-CON.tv interview at @DevOpsSummit (http://DevOpsSummit.SYS-CON.com), held June 9-11, 2015, at the Javits Center in New York
Jul. 1, 2015 02:45 PM EDT Reads: 1,100
Discussions about cloud computing are evolving into discussions about enterprise IT in general. As enterprises increasingly migrate toward their own unique clouds, new issues such as the use of containers and microservices emerge to keep things interesting. In this Power Panel at 16th Cloud Expo, moderated by Conference Chair Roger Strukhoff, panelists addressed the state of cloud computing today, and what enterprise IT professionals need to know about how the latest topics and trends affect t...
Jul. 1, 2015 02:30 PM EDT Reads: 1,209
Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In his session at @ThingsExpo, James Kirkland, Red Hat's Chief Arch...
Jul. 1, 2015 02:21 PM EDT Reads: 687
In the midst of the widespread popularity and adoption of cloud computing, it seems like everything is being offered “as a Service” these days: Infrastructure? Check. Platform? You bet. Software? Absolutely. Toaster? It’s only a matter of time. With service providers positioning vastly differing offerings under a generic “cloud” umbrella, it’s all too easy to get confused about what’s actually being offered. In his session at 16th Cloud Expo, Kevin Hazard, Director of Digital Content for SoftL...
Jul. 1, 2015 01:15 PM EDT Reads: 2,179
"A lot of the enterprises that have been using our systems for many years are reaching out to the cloud - the public cloud, the private cloud and hybrid," stated Reuven Harrison, CTO and Co-Founder of Tufin, in this SYS-CON.tv interview at 16th Cloud Expo, held June 9-11, 2015, at the Javits Center in New York City.
Jul. 1, 2015 12:54 PM EDT Reads: 649
One of the hottest areas in cloud right now is DRaaS and related offerings. In his session at 16th Cloud Expo, Dale Levesque, Disaster Recovery Product Manager with Windstream's Cloud and Data Center Marketing team, will discuss the benefits of the cloud model, which far outweigh the traditional approach, and how enterprises need to ensure that their needs are properly being met.
Jul. 1, 2015 12:15 PM EDT Reads: 2,062
The time is ripe for high speed resilient software defined storage solutions with unlimited scalability. ISS has been working with the leading open source projects and developed a commercial high performance solution that is able to grow forever without performance limitations. In his session at Cloud Expo, Alex Gorbachev, President of Intelligent Systems Services Inc., shared foundation principles of Ceph architecture, as well as the design to deliver this storage to traditional SAN storage co...
Jul. 1, 2015 12:00 PM EDT Reads: 2,022
"Plutora provides release and testing environment capabilities to the enterprise," explained Dalibor Siroky, Director and Co-founder of Plutora, in this SYS-CON.tv interview at @DevOpsSummit, held June 9-11, 2015, at the Javits Center in New York City.
Jul. 1, 2015 11:45 AM EDT Reads: 1,050
SYS-CON Events announced today that JFrog, maker of Artifactory, the popular Binary Repository Manager, will exhibit at SYS-CON's @DevOpsSummit Silicon Valley, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Based in California, Israel and France, founded by longtime field-experts, JFrog, creator of Artifactory and Bintray, has provided the market with the first Binary Repository solution and a software distribution social platform.
Jul. 1, 2015 11:30 AM EDT Reads: 1,004
It is one thing to build single industrial IoT applications, but what will it take to build the Smart Cities and truly society-changing applications of the future? The technology won’t be the problem, it will be the number of parties that need to work together and be aligned in their motivation to succeed. In his session at @ThingsExpo, Jason Mondanaro, Director, Product Management at Metanga, discussed how you can plan to cooperate, partner, and form lasting all-star teams to change the world...
Jul. 1, 2015 11:30 AM EDT Reads: 2,261
In his session at 16th Cloud Expo, Simone Brunozzi, VP and Chief Technologist of Cloud Services at VMware, reviewed the changes that the cloud computing industry has gone through over the last five years and shared insights into what the next five will bring. He also chronicled the challenges enterprise companies are facing as they move to the public cloud. He delved into the "Hybrid Cloud" space and explained why every CIO should consider ‘hybrid cloud' as part of their future strategy to achi...
Jul. 1, 2015 11:10 AM EDT Reads: 718
"We got started as search consultants. On the services side of the business we have help organizations save time and save money when they hit issues that everyone more or less hits when their data grows," noted Otis Gospodnetić, Founder of Sematext, in this SYS-CON.tv interview at @DevOpsSummit, held June 9-11, 2015, at the Javits Center in New York City.
Jul. 1, 2015 11:00 AM EDT Reads: 974
Internet of Things is moving from being a hype to a reality. Experts estimate that internet connected cars will grow to 152 million, while over 100 million internet connected wireless light bulbs and lamps will be operational by 2020. These and many other intriguing statistics highlight the importance of Internet powered devices and how market penetration is going to multiply many times over in the next few years.
Jul. 1, 2015 10:30 AM EDT Reads: 2,150
Internet of Things (IoT) will be a hybrid ecosystem of diverse devices and sensors collaborating with operational and enterprise systems to create the next big application. In their session at @ThingsExpo, Bramh Gupta, founder and CEO of robomq.io, and Fred Yatzeck, principal architect leading product development at robomq.io, discussed how choosing the right middleware and integration strategy from the get-go will enable IoT solution developers to adapt and grow with the industry, while at th...
Jul. 1, 2015 09:45 AM EDT Reads: 1,957
The most often asked question post-DevOps introduction is: “How do I get started?” There’s plenty of information on why DevOps is valid and important, but many managers still struggle with simple basics for how to initiate a DevOps program in their business. They struggle with issues related to current organizational inertia, the lack of experience on Continuous Integration/Delivery, understanding where DevOps will affect revenue and budget, etc. In their session at DevOps Summit, JP Morgenthal...
Jul. 1, 2015 09:32 AM EDT Reads: 678