Database (R)evolutions : The Third Wave


the-database-revolution

Background on the (R)Evolution of Modern Databases

The first wave of database revolution involved the Hierarchical and network database systems that dominated he era of mainframe computing and
powered the vast majority of computer applications up until the late 1970s (think COBOL).

The second wave of database revolution was primarily influenced by the relational theory developed by Edgar Boyce Codd. Example applications include MSSQL, Ingress, Postgress, mySQL etc.

By 2005 the emergence of massive web-scale applications created pressures on the relational database as it was found inadequate to deal with the volumes and velocity of the data confronting the likes of Google. The challenges that enterprises face with “big data” today are problems that Google first encountered almost 20 years ago. Very early on, Google had to invent new hardware and software architectures to store and process the
exponentially growing quantity of websites it needed to index.

In 2003, Google revealed details of the distributed Google file system (GFS) that formed a foundation for its storage architectures and in 2004 it revealed details of the distributed parallel processing algorithm MapReduce, which was used to create World Wide Web indexes.In 2006, Google revealed details about its BigTable distributed structured database.These concepts, together with other technologies, many of which also came from Google, formed the basis for the Hadoop project, which matured within Yahoo! and which experienced rapid uptake from 2007 on. The Hadoop ecosystem more than anything else became a technology enabler for the Big Data ecosystem

Mean while The Rest of the Web….

While Google had an overall scale of operation and data volume way beyond that of any other web company,other websites had challenges of their own. Websites dedicated to online e-commerce—Amazon, for example—had a need for a transactional processing capability that could operate at massive scale. Early social networking sites such as MySpace and eventually Facebook faced similar challenges in scaling their
infrastructure from thousands to millions of users. Again, even the most expensive commercial RDBMS such as Oracle could not provide sufficient scalability to meet the demands of these sites. Oracle’s scaled-out RDBMS architecture (Oracle RAC) attempted to provide a road-map for limitless scalability, but it was economically unattractive and never seemed to offer the scale required at the leading edge.

Many early websites attempted to scale open-source databases through a variety of do-it-yourself techniques. This involved utilizing distributed object cases such as Memcached to offload database load, database replication to spread database read activity, and eventually—when all else failed—“Sharding.”

Sharding involves partitioning the data across multiple databases based on a key attribute, such as the customer identifier. For instance, in Twitter and Facebook, customer data is split up across a very large number of MySQL databases. Most data for a specific user ends up on the one database, so that operations for a specific customer are quick. It’s up to the application to work out the correct shard and to route requests appropriately.
Sharding at sites like Facebook has allowed a MySQL-based system to scale up to massive levels, but the downsides of doing this are immense. Many relational operations and database-level ACID transactions are lost. It becomes impossible to perform joins or maintain transactional integrity across shards. The operational costs of sharding, together with the loss of relational features, made many seek alternatives to the RDBMS.

Meanwhile, a similar dilemma within Amazon had resulted in development of an alternative model to strict ACID consistency within its homegrown data store. Amazon revealed details of this system, “Dynamo,” in 2008.Amazon’s Dynamo model, together with innovations from web developers seeking a “webscale” database, led to the emergence of what came to be known as key-value databases.

Cloud Computing

The existence of applications and databases “in the cloud”—that is, accessed from the Internet—had been a persistent feature of the application landscape since the late 1990s. However, around 2008, cloud computing erupted somewhat abruptly as a major concern for large organizations and a huge opportunity for startups.
For the previous 5 to 10 years, mainstream adoption of computer applications had shifted from rich desktop applications based on the client-server model to web-based applications whose data stores and application servers resided somewhere accessible via the Internet—“the cloud.” This created a real challenge for emerging companies that needed somehow to establish sufficient hosting for early adopters, as well as the ability to scale up rapidly should they experience the much-desired exponential growth.

Between 2006 and 2008, Amazon rolled out Elastic Compute Cloud (EC2). EC2 made available virtual machine images hosted on Amazon’s hardware infrastructure and accessible via the Internet. EC2 could be used to host web applications, and computing power could be relatively rapidly added on demand.

Amazon added other services such as storage (S3, EBS), Virtual Private Cloud (VPC), a MapReduce service (EMR), and so on. The entire platform was known as Amazon Web Services (AWS) and was the first practical implementation of an Infrastructure as a Service (IaaS) cloud. AWS became the inspiration for cloud computing offerings from Google, Microsoft, and others.  For applications wishing to exploit the elastic scalability allowed by cloud computing platforms, existing relational databases were a poor fit. Oracle’s attempts to integrate grid computing into its architecture had met with only limited success and were economically and practically inadequate for these applications,
which needed to be able to expand on demand. That demand for elastically scalable databases fueled the demand generated by web-based startups and accelerated the growth of key-value stores, often based on Amazon’s own Dynamo design. Indeed, Amazon offered nonrelational services in its cloud starting with SimpleDB, which eventually was replaced by DynamoDB.

Document Databases

Programmers continued to be unhappy with the impedance mismatch between object-oriented and relational models. Object relational mapping systems only relieved a small amount of the inconvenience that occurred when a complex object needed to be stored on a relational database in normal form.
Starting about 2004, an increasing number of websites were able to offer a far richer interactive experience than had been the case previously. This was enabled by the programming style known as AJAX (Asynchronous JavaScript and XML), in which JavaScript within the browser communicates directly with a backend by transferring XML messages. XML was soon superseded by JavaScript Object Notation (JSON), which is a self-describing format similar to XML but is more compact and tightly integrated into the
JavaScript language. JSON became the de facto format for storing—serializing—objects to disk. Some websites started storing JSON documents directly into columns within relational tables. It was only a matter of time before someone decided to eliminate the relational middleman and create a database in which JSON could be directly stored. These became known as document databases.

CouchBase and MongoDB are two popular JSON-oriented databases, though virtually all nonrelational databases—and most relational databases, as well—support JSON. Programmers like document databases for the same reasons they liked OODBMS: it relieves them of the laborious process of translating objects to relational format.

The “NewSQL”

Neither the relational nor the ACID transaction model dictated the physical architecture for a relational database. However, partly because of a shared ancestry and partly because of the realities of the hardware of the day, most relational databases ended up being implemented in a very similar manner. The format of data on disk, the use of memory, the nature of locks, and so on varied only slightly among the major RDBMS implementations.
In 2007, Michael Stonebraker, pioneer of the Ingres and Postgres database systems, led a research team that published the seminal paper “The End of an Architectural Era (It’s Time for a Complete Rewrite).” This paper pointed out that the hardware assumptions that underlie the consensus relational architecture no longer applied, and that the variety of modern database workloads suggested a single architecture might not be optimal across all workloads. Stonebraker and his team proposed a number of variants on the existing RDBMS design, each of which was optimized for a specific application workload. Two of these designs became particularly significant (although to be fair, neither design was necessarily completely unprecedented). H-Store described a pure inmemory
distributed database while C-Store specified a design for a columnar database. Both these designs were extremely influential in the years to come and are the first examples of what came to be known as NewSQL database systems—databases that retain key characteristics of the RDBMS but that diverge from the common architecture exhibited by traditional systems such as Oracle and SQL Server.

The Non-relational Explosion

rdbms-history

Figure 1. Timeline of major database releases and innovations

As we see in Figure 1, a huge number of relational database systems emerged in the first half of the  2000s. In particular, a sort of “Cambrian explosion” occurred in the years 2008–2009: literally dozens of new database systems emerged in this short period. Many of these have fallen into disuse, but some—such as MongoDB, Cassandra, and HBase—have today captured significant market share.
At first, these new breeds of database systems lacked a common name. “Distributed Non-Relational Database Management System” (DNRDBMS) was proposed, but clearly wasn’t going to capture anybody’s imagination. However, in late 2009, the term NoSQL quickly caught on as shorthand for any database system that broke with the traditional SQL database.

In the opinion of many, NoSQL is an unfortunate term: it defines what a database is not rather than what it is, and it focuses attention on the presence or absence of the SQL language. Although it’s true that most nonrelational systems do not support SQL, actually it is variance from the strict transactional and relational data model that motivated most NoSQL database designs.

By 2011, the term NewSQL became popularized as a means of describing this new breed of databases that, while not representing a complete break with the relational model, enhanced or significantly modified Finally, the term Big Data burst onto mainstream consciousness in early 2012. Although the term refers mostly to the new ways in which data is being leveraged to create value, we generally understand “Big Data solutions” as convenient shorthand for technologies that support large and unstructured datasets such as Hadoop.

Note NoSQL, NewSQL, and Big Data are in many respects vaguely defined, overhyped, and overloaded terms. However, they represent the most widely understood phrases for referring to next-generation database technologies.

Loosely speaking, NoSQL databases reject the constraints of the relational model, including strict consistency and schemas. NewSQL databases retain many features of the relational model but amend the underlying technology in significant ways. Big Data systems are generally oriented around technologies within the Hadoop ecosystem, increasingly including Spark.

Conclusion: One Size Doesn’t Fit All

Verbat Ltd

The first database revolution arose as an inevitable consequence of the emergence of electronic digital computers. In some respect, the databases of the first wave were electronic analogs of pre-computer technologies such as punched cards and tabulating machines. Early attempts to add a layer of structure and consistency to these databases may have improved programmer efficiency and data consistency, but they left the data locked in systems to which only programmers held the keys.

The second database revolution resulted from Edgar Codd’s realization that database systems would be well served if they were based on a solid, formal, and mathematical foundation; that the representation of data should be independent of the physical storage implementation; and that databases should support flexible query mechanisms that do not require sophisticated programming skills. The successful development of the modern relational database over such an extended time —more than 30 years of commercial dominance—represents a triumph of computer science and software engineering. Rarely has a software theoretical concept been so successfully and widely implemented as the relational database.

The third database revolution is not based on a single architectural foundation. If anything, it rests on the proposition that a single database architecture cannot meet the challenges posed in our modern digital world. The existence of massive social networking applications with hundreds of millions of users and the emergence of Internet of Things (IoT) applications with potentially billions of machine inputs, strain the relational database—and particularly the ACID transaction model—to the breaking point. At the other end of the scale we have applications that must run on mobile and wearable devices with limited memory and computing power. And we are awash with data, much of which is of unpredictable structure for which rendering to relational form is untenable. The third wave of databases roughly corresponds to a third wave of computer applications. IDC and
others often refer to this as “the third platform.” The first platform was the mainframe, which was supported by pre-relational database systems. The second platform, client-server and early web applications, was supported by relational databases. The third platform is characterized by applications that involve cloud deployment, mobile presence, social networking, and the Internet of Things. The third platform demands a third wave of database technologies that include but are not limited to relational systems. Figure  2 summarizes how the three platforms correspond to the waves of database revolutions.

dbrevolution

Figure 2. The three waves of database technology

Credits: Guy Harrison,  Next Generation Databases

 

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