Welcome!

Agile Computing Authors: James Carlini, Ferhat Hatay, Charlotte Spencer-Smith, Elizabeth White, Pat Romanski

Related Topics: @CloudExpo, Java IoT, Microservices Expo, Containers Expo Blog, @BigDataExpo, SDN Journal

@CloudExpo: Article

Can We Finally Find the Database Holy Grail? | Part 3

With the advent of Durable Distributed Cache architectures organizations can build global systems with transactional semantics

In my first post in this three part series I talked about the need for distributed transactional databases that scale-out horizontally across commodity machines, as compared to traditional transactional databases that employ a "scale-up" design.  Simply adding more machines is a quicker, cheaper and more flexible way of increasing database capacity than forklift upgrades to giant steam-belching servers. It also brings the promise of continuous availability and of geo-distributed operation.

The second post in this series provided an overview of the three historical approaches to designing distributed transactional database systems, namely: 1. Shared Disk Designs (e.g., ORACLE RAC); 2. Shared Nothing Designs (e.g. the Facebook MySQL implementation); and 3) Synchronous Commit Designs (e.g. GOOGLE F1).  All of them have some advantages over traditional client-server database systems, but they each have serious limitations in relation to cost, complexity, dependencies on specialized infrastructure, and workload-specific performance trade-offs. I noted that we are very excited about a recent innovation in distributed database design, introduced by NuoDB's technical founder Jim Starkey.  We call the concept Durable Distributed Cache (DDC), and I want to spend a little time in this third and final post talking about what it is, with a high-level overview of how it works.

Memory-Centric vs. Storage-Centric
The first insight Jim had was that all general-purpose relational databases to-date have been architected around a storage-centric assumption, and that this is a fundamental problem when it comes to scaling out.  In effect, database systems have been fancy file systems that arrange for concurrent read/write access to disk-based files such that users do not trample on each other.  The Durable Distributed Cache architecture inverts that idea, imagining the database as a set of in-memory container objects that can overflow to disk if necessary, and can be retained in backing stores for durability purposes.  Memory-Centric vs. Storage-Centric may sound like splitting hairs, but it turns out that it is really significant.  The reasons are best described by example.

Suppose you have a single, logical DDC database running on 50 servers (which is absolutely feasible to do with an ACID transactional DDC-based database).  And suppose that at some moment server 23 needs object #17.  In this case, server 23 might determine that object #17 is instantiated in memory on seven other servers.  It simply requests the object from the most responsive server.  Note that as the object was in memory, the operation involved no disk IO - it was a remote memory fetch, which is orders of magnitude faster than going to disk.

You might ask about the case in which object #17 does not exist in memory elsewhere.  In the Durable Distributed Cache architecture this is handled by certain servers "faking" that they have all the objects in memory.  In practice, of course, they are maintaining backing stores on disk, SSD or whatever they choose (in the NuoDB implementation they can use arbitrary Key/Value stores such as Amazon S3 or Hadoop HDFS).  As it relates to supplying objects, these "backing store servers" behave exactly like the other servers except they can't guarantee the same response times.

So all servers in the DDC architecture can request objects and supply objects.  They are peers in that sense (and in all other senses).  Some servers have a subset of the objects at any given time, and can therefore only supply a subset of the database to other servers.  Other servers have all the objects and can supply any of them, but will be slower to supply objects that are not resident in memory.

Let's call the servers with a subset of the objects Transaction Engines (TEs), and the other servers Storage Managers (SMs).  TEs are pure in memory servers that do not need to use disks.  They are autonomous and can unilaterally load and eject objects from memory according to their needs.  Unlike TEs, SMs can't just drop objects on the floor when they are finished with them; instead they must ensure they are safely placed in durable storage.

For readers familiar with caching architectures, you might have already recognized that these TEs are in effect a distributed DRAM cache, and the SMs are specialized TEs that ensure durability.  Hence the name Durable Distributed Cache.

Resilience to Failure
It turns out that any object state that is present on a TE is either already committed to the disk (i.e. safe on one or more SMs) or part of an uncommitted transaction that will simply fail at application level if the object goes away. This means that the database has the interesting property of being resilient to the loss of TEs.  You can shut a TE down or just unplug it and the system does not lose data.  It will lose throughput capacity of course, and any partial transactions on the TE will be reported to the application as failed transactions.  But transactional applications are designed to handle transaction failure. If you reissue the transaction at the application level it will be assigned to a different TE and will proceed to completion.  So the DDC architecture is resilient to the loss of TEs.

What about SMs?  Recall that you can have as many SMs as you like.  They are effectively just TEs that secretly stash away the objects in some durable store.  And, unless you configure it not to, each SM might as well store all the objects. Disks are cheap, which means that you have as many redundant copies of the whole database as you want.  In consequence, the DDC architecture is not only resilient to the loss of TEs, but also to the loss of SMs.

In fact, as long as you have at least one TE and one SM running, you still have a running database.  Resilience to failure is one of the longstanding but unfulfilled promises of distributed transactional databases.  The DDC architecture addresses this directly.

Elastic Scale-out and Scale-in
What happens if I add a server to a DDC database?  Think of the TE layer as a cache.  If the new TE is given work to do, it will start asking for objects and doing the assigned work.  It will also start serving objects to other TEs that need them.  In fact, the new TE is a true peer of the other TEs.  Furthermore, if you were to shut down all of the other TEs, the database would still be running, and the new TE would be the only server doing transactional work.

SMs, being specialized TEs, can also be added and shut down dynamically.  If you add an "empty" (or stale) SM to a running database, it will cycle through the list of objects and load them into its durable store, fetching them from the most responsive place as is usual.  Once it has all the objects, it will raise its hand and take part as a peer to the other SMs.  And, just as with the new TE described above, you can delete all other SMs once you have added the new SM.  The system will keep running without missing a beat or losing any data.

So the bottom line is that the DDC architecture delivers capacity on demand.  You can elastically scale-out the number of TEs and SMs and scale them back in again according to workload requirements.  Capacity on demand is a second promise of distributed databases that is delivered by the DDC architecture.

Geo-Distribution
The astute reader will no doubt be wondering about the hardest part of this distributed database problem -- namely that we are talking about distributed transactional databases.  Transactions, specifically ACID transactions, are an enormously simplifying abstraction that allows application programmers to build their applications with very clean, high-level and well-defined data guarantees.  If I store my data in an ACID transactional database, I know it will isolate my program from other programs, maintain data consistency, avoid partial failure of state changes and guarantee that stored data will still be there at a later date, irrespective of external factors.  Application programs are vastly simpler when they can trust an ACID compliant database to look after their data, whatever the weather.

The DDC architecture adopts a model of append-only updates.  Traditionally, an update to a record in a database overwrites that record, and a deletion of a record removes the record.  That may sound obvious, but there is another way, invented by Jim Starkey about 25 years ago.  The idea is to create and maintain versions of everything.  In this model, you never do a destructive update or destructive delete.  You only ever create new versions of records, and in the case of a delete, the new version is a record version that notes the record is no longer extant.  This model is called MVCC (multi-version concurrency control), and it has a number of well-known benefits, even in scale-up databases.  MVCC has even greater benefits in distributed database architectures, including DDC.

We don't have the space here to cover MVCC in detail, but it is worth noting that one of the things it does is to allow a DBMS to manage read/write concurrency without the use of traditional locks.  For example, readers don't block writers and writers do not block readers.  It also has some exotic features, including that if you wanted to you could theoretically maintain a full history of the entire database.  But as it relates to DDC and the Distributed Transactional Database challenge, there is something very neat about MVCC.  DDC leverages a distributed variety of MVCC in concert with DDC's distributed object semantics that allows almost all the inter-server communications to be asynchronous.

The implications of DDC being asynchronous are very far-reaching.  In general, it allows much higher utilization of system resources (cores, networks, disks, etc.) than synchronous models can.  But specifically, it allows the system to be fairly insensitive to network latencies, and to the location of the servers relative to each other.  Or to put it a different way, it means you can start up your next TE or SM in a remote datacenter and connect it to the running database.  Or you can start up half of the database servers in your datacenter and the other half on a public cloud.

Modern applications are distributed.  Users of a particular web site are usually spread across the globe.  Mobile applications are geo-distributed by nature.  Internet of Things (IoT) applications are connecting gazillions of consumer devices that could be anywhere at any time.  None of these applications are well served by a single big database server in a single location, or even a cluster of smaller database servers in a single location.  What they need is a single database running on a group of database servers in multiple datacenters (or cloud regions).  That can give them higher performance, datacenter failover and the potential to manage issues of data privacy and sovereignty.

The third historical promise of Distributed Transactional Database systems is Geo-Distribution.  Along with the other major promises (Resilience to Failure and Elastic Scalability), Geo-Distribution has heretofore been an unattainable dream.  The DDC architecture, with its memory-centric distributed object model and its asynchronous inter-server protocols, finally delivers on this capability.

In Summary
This short series of posts has sought to provide a quick overview of distributed database designs, with some high level commentary on the advantages and disadvantages of the various approaches.  There has been great historical success with Shared Disk, Shared Nothing and Synchronous Commit models.  We see the advanced technology companies delivering some of the most scalable systems in the world using these distributed database technologies.  But to date, distributed databases have never really delivered anything close to their full promise.  They have also been inaccessible to people and organizations that lack the development and financial resources of GOOGLE or Facebook.

With the advent of DDC architectures, it is now possible for any organization to build global systems with transactional semantics, on-demand capacity and the ability to run for 10 years without missing a beat.  The big promises of Distributed Transactional Databases are Elastic Scalability and Geo-Distribution.  We're very excited that due to Jim Starkey's Durable Distributed Cache, those capabilities are finally being delivered to the industry.

More Stories By Barry Morris

Barry Morris is CEO & Co-Founder of NuoDB, Inc. An accomplished software CEO with over 25 years of industry experience in the USA and Europe, running private and public companies ranging in scale from early startup phase to 1,000+ employees, he loves to build companies around industry-changing paradigm-shifts in technology. Morris was previously CEO of StreamBase and Iona Technologies.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@ThingsExpo Stories
The cloud promises new levels of agility and cost-savings for Big Data, data warehousing and analytics. But it’s challenging to understand all the options – from IaaS and PaaS to newer services like HaaS (Hadoop as a Service) and BDaaS (Big Data as a Service). In her session at @BigDataExpo at @ThingsExpo, Hannah Smalltree, a director at Cazena, will provide an educational overview of emerging “as-a-service” options for Big Data in the cloud. This is critical background for IT and data profes...
One of the bewildering things about DevOps is integrating the massive toolchain including the dozens of new tools that seem to crop up every year. Part of DevOps is Continuous Delivery and having a complex toolchain can add additional integration and setup to your developer environment. In his session at @DevOpsSummit at 18th Cloud Expo, Miko Matsumura, Chief Marketing Officer of Gradle Inc., will discuss which tools to use in a developer stack, how to provision the toolchain to minimize onboa...
Companies can harness IoT and predictive analytics to sustain business continuity; predict and manage site performance during emergencies; minimize expensive reactive maintenance; and forecast equipment and maintenance budgets and expenditures. Providing cost-effective, uninterrupted service is challenging, particularly for organizations with geographically dispersed operations.
SYS-CON Events announced today that Interoute, owner-operator of one of Europe's largest networks and a global cloud services platform, has been named “Bronze Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2015 at the Javits Center in New York, New York. Interoute is the owner-operator of one of Europe's largest networks and a global cloud services platform which encompasses 12 data centers, 14 virtual data centers and 31 colocation centers, with connections to 195 ad...
Join us at Cloud Expo | @ThingsExpo 2016 – June 7-9 at the Javits Center in New York City and November 1-3 at the Santa Clara Convention Center in Santa Clara, CA – and deliver your unique message in a way that is striking and unforgettable by taking advantage of SYS-CON's unmatched high-impact, result-driven event / media packages.
SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Commvault is a leading provider of data protection and information management...
There will be new vendors providing applications, middleware, and connected devices to support the thriving IoT ecosystem. This essentially means that electronic device manufacturers will also be in the software business. Many will be new to building embedded software or robust software. This creates an increased importance on software quality, particularly within the Industrial Internet of Things where business-critical applications are becoming dependent on products controlled by software. Qua...
With an estimated 50 billion devices connected to the Internet by 2020, several industries will begin to expand their capabilities for retaining end point data at the edge to better utilize the range of data types and sheer volume of M2M data generated by the Internet of Things. In his session at @ThingsExpo, Don DeLoach, CEO and President of Infobright, will discuss the infrastructures businesses will need to implement to handle this explosion of data by providing specific use cases for filte...
SYS-CON Events announced today that Pythian, a global IT services company specializing in helping companies adopt disruptive technologies to optimize revenue-generating systems, has been named “Bronze Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2015 at the Javits Center in New York, New York. Founded in 1997, Pythian is a global IT services company that helps companies compete by adopting disruptive technologies such as cloud, Big Data, advanced analytics, and DevO...
SYS-CON Events announced today that Avere Systems, a leading provider of enterprise storage for the hybrid cloud, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Avere delivers a more modern architectural approach to storage that doesn’t require the overprovisioning of storage capacity to achieve performance, overspending on expensive storage media for inactive data or the overbuilding of data centers ...
SYS-CON Events announced today that Alert Logic, Inc., the leading provider of Security-as-a-Service solutions for the cloud, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Alert Logic, Inc., provides Security-as-a-Service for on-premises, cloud, and hybrid infrastructures, delivering deep security insight and continuous protection for customers at a lower cost than traditional security solutions. Ful...
Fortunately, meaningful and tangible business cases for IoT are plentiful in a broad array of industries and vertical markets. These range from simple warranty cost reduction for capital intensive assets, to minimizing downtime for vital business tools, to creating feedback loops improving product design, to improving and enhancing enterprise customer experiences. All of these business cases, which will be briefly explored in this session, hinge on cost effectively extracting relevant data from ...
SYS-CON Events announced today that iDevices®, the preeminent brand in the connected home industry, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. iDevices, the preeminent brand in the connected home industry, has a growing line of HomeKit-enabled products available at the largest retailers worldwide. Through the “Designed with iDevices” co-development program and its custom-built IoT Cloud Infrastruc...
As enterprises work to take advantage of Big Data technologies, they frequently become distracted by product-level decisions. In most new Big Data builds this approach is completely counter-productive: it presupposes tools that may not be a fit for development teams, forces IT to take on the burden of evaluating and maintaining unfamiliar technology, and represents a major up-front expense. In his session at @BigDataExpo at @ThingsExpo, Andrew Warfield, CTO and Co-Founder of Coho Data, will dis...
The Quantified Economy represents the total global addressable market (TAM) for IoT that, according to a recent IDC report, will grow to an unprecedented $1.3 trillion by 2019. With this the third wave of the Internet-global proliferation of connected devices, appliances and sensors is poised to take off in 2016. In his session at @ThingsExpo, David McLauchlan, CEO and co-founder of Buddy Platform, will discuss how the ability to access and analyze the massive volume of streaming data from mil...
WebSocket is effectively a persistent and fat pipe that is compatible with a standard web infrastructure; a "TCP for the Web." If you think of WebSocket in this light, there are other more hugely interesting applications of WebSocket than just simply sending data to a browser. In his session at 18th Cloud Expo, Frank Greco, Director of Technology for Kaazing Corporation, will compare other modern web connectivity methods such as HTTP/2, HTTP Streaming, Server-Sent Events and new W3C event APIs ...
SYS-CON Events announced today that Men & Mice, the leading global provider of DNS, DHCP and IP address management overlay solutions, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. The Men & Mice Suite overlay solution is already known for its powerful application in heterogeneous operating environments, enabling enterprises to scale without fuss. Building on a solid range of diverse platform support,...
Eighty percent of a data scientist’s time is spent gathering and cleaning up data, and 80% of all data is unstructured and almost never analyzed. Cognitive computing, in combination with Big Data, is changing the equation by creating data reservoirs and using natural language processing to enable analysis of unstructured data sources. This is impacting every aspect of the analytics profession from how data is mined (and by whom) to how it is delivered. This is not some futuristic vision: it's ha...
Silver Spring Networks, Inc. (NYSE: SSNI) extended its Internet of Things technology platform with performance enhancements to Gen5 – its fifth generation critical infrastructure networking platform. Already delivering nearly 23 million devices on five continents as one of the leading networking providers in the market, Silver Spring announced it is doubling the maximum speed of its Gen5 network to up to 2.4 Mbps, increasing computational performance by 10x, supporting simultaneous mesh communic...
With the Apple Watch making its way onto wrists all over the world, it’s only a matter of time before it becomes a staple in the workplace. In fact, Forrester reported that 68 percent of technology and business decision-makers characterize wearables as a top priority for 2015. Recognizing their business value early on, FinancialForce.com was the first to bring ERP to wearables, helping streamline communication across front and back office functions. In his session at @ThingsExpo, Kevin Roberts...