Transactional integrity is part and parcel of the mainframe era, but it is undergoing some shifts in the age of the Web. Development leaders are finding this as throngs of front-end Web users 'hit' the back-end mainframe. It is left up to the software architect to balance dueling system objectives.
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Going forward, both the mainframe and the Web front-end have distinct roles to play, according to a noted industry analyst. James Governor, principal analyst and founder of RedMonk, spoke about mainframe transaction processing at IBM Impact 2012 in Las Vegas in a session on IBM's Z-series and transactional integrity issues.
Software designers should work to gain a good understanding of those roles in order to succeed with increasingly stressed Web application architectures, Governor stated.
“Scale really is going gangbusters,” he exclaimed. The growing “Internet of things” and a big rush of smartphone-style devices will stress systems, he indicated.
Workloads are going up significantly, a large mainframe user agreed. But the mainframe supporting a key lodging system can handle the load, said Misha Kravchenko, vice president, Information Services, Marriott International.
Kravchenko estimates that Marriott books 800,000 room-nights every day using a central operations system that “has no down time.” This workload has gone up in recent years, as Marriott strived to consolidate distributed workloads on an IBM Z-class machine. Clearly, the Web has been a disruptive force in a business that was once largely dependent on call centers, travel agents and the plain old telephone.
He anticipates further dramatic increases upcoming when mobile applications truly take off. Marriott has recently released mobile tools that help travelers find nearby hotels, book rooms and check on reservations. Many of these mobile users are part of the Marriott Rewards program.
Central to understanding the issue of transactions, said analyst Governor, is an understanding of the ''CAP'' theorem of computer scientist Eric Brewer. ''CAP'' here stands for ''Consistency-Availability-Partition Tolerance.''
Brewer concluded that a system designer could typically only mandate two of these three traits in a design. Cloud poster child Amazon.com is famous for putting ''eventual consistency'' ahead of immediate transactional consistency in its flagship e-commerce system.
The mainframe crew takes a much different view of these transactional traits. In Governor’s words: ''Mainframe people want all three.''
High-integrity transaction processing, big iron and punk rock
Software architects may do well to consider the mainframe for the class of transactions that needs all three of Brewer’s traits, but consider isolating other activity. They might consider standalone ESB gateways for some parts of the job. They may also look to avoid undue round trips for XML data, in Marriott IT manager Kravchenko’s estimation.
In an earlier version of his central lodging system, a single XML transaction would go to the mainframe four or five times, Kravchenko said. That has changed.
“Now the XML messages are done in the mainframe. That means less trips,” he said. At the same time, because of less back and forth, the use of mainframe MIPS went down, he indicated.
The nature of the Marriott system’s transactions are different than those of e-commerce site Amazon. An understanding of this confirmed Marriott’s plan to closely couple transaction processing with a room inventory database.
When you go shopping at Amazon for a book, you don’t see the inventory, which is updated every now and then, and which can be described as an eventually consistent aspect of the transaction. This is okay for Amazon, in Kravchenko’s opinion, because the price of a book, for example, does not change too much, and delayed availability can be acceptable if communications with the customer are properly handled.
A hotel room is different; its immediate, guaranteed availability can be crucial - as most business travelers have discovered on certain dark and stormy nights.
Marriott, like others, has carefully calculated elastic pricing on blocks of rooms. This ''revenue management pricing system is complex, and the company needs pricing “right down to the last room,” said Kravchenko.
“We need one database. It is connected with inventory. Amazon is different,” he said.
The cloud transactional style can cover a lot - but not all - ground.
In a way, cloud purveyors have rebuilt mainframe-style transaction processing for the Web era. Governor adroitly summed up the new transaction firmament using a music analogy: “The young Turks have come up here and built their systems. They are trying to do what the mainframe did."
The Amazons, Googles and Facebooks have taken a simpler approach that stripped down complexity, much as punk music in the 1970's recast rock' n' roll.
“They said ‘we will do it with just four chords',” joked Governor.
Regarding mainframes, Governor said, “let’s understand what they are best at, and possibly learn some from the punks.”