Questioning the Lambda Architecture

http://radar.oreilly.com/2014/07/questioning-the-lambda-architecture.html

The problem with the Lambda Architecture is that maintaining code that needs to produce the same result in two complex distributed systems is exactly as painful as it seems like it would be. I don’t think this problem is fixable. Programming in distributed frameworks like Storm and Hadoop is complex. Inevitably, code ends up being specifically engineered toward the framework it runs on. The resulting operational complexity of systems implementing the Lambda Architecture is the one thing that seems to be universally agreed on by everyone doing it.(两个系统差别巨大,维护在两个系统下运行的代码,并且确保输出结果一致是非常困难的)

One proposed approach to fixing this is to have a language or framework that abstracts over both the real-time and batch framework. You write your code using this higher level framework and then it “compiles down” to stream processing or MapReduce under the covers. Summingbird is a framework that does this. This definitely makes things a little better, but I don’t think it solves the problem.(一种解决办法是使用类似SummingBird框架使用一份代码)

Ultimately, even if you can avoid coding your application twice, the operational burden of running and debugging two systems is going to be very high. And any new abstraction can only provide the features supported by the intersection of the two systems. Worse, committing to this new uber-framework walls off the rich ecosystem of tools and languages that makes Hadoop so powerful (Hive, Pig, Crunch, Cascading, Oozie, etc).(即使能够避免写两份代码,也存在许多问题:1. 运维两套系统非常困难 2. 这个框架功能只能取两者交集 3. 框架使得许多现有优秀工具无法使用)

By way of analogy, consider the notorious difficulties in making cross-database ORM really transparent. And consider that this is just a matter of abstracting over very similar systems providing virtually identical capabilities with a (nearly) standardized interface language. The problem of abstracting over totally divergent programming paradigms built on top of barely stable distributed systems is much harder.(想想ORM对试图屏蔽关系数据库的努力吧!)

We have actually been through a number of rounds of this at LinkedIn. We have built various hybrid-Hadoop architectures and even a domain-specific API that would allow code to be “transparently” run either in real time or in Hadoop. These approaches worked, but none were very pleasant or productive. Keeping code written in two different systems perfectly in sync was really, really hard. The API meant to hide the underlying frameworks proved to be the leakiest of abstractions. It ended up requiring deep Hadoop knowledge as well as deep knowledge of the real-time layer — and adding the new requirement that you understand enough about how the API would translate to these underlying systems whenever you were debugging problems or trying to reason about performance. These days, my advice is to use a batch processing framework like MapReduce if you aren’t latency sensitive, and use a stream processing framework if you are, but not to try to do both at the same time unless you absolutely must.(从我们的经验上看,这种框架是非常难做到的,即便是做到了也非常难用。抽象层的API不能很好地完全屏蔽细节,用户依然要深入了解Hadoop和实时系统。如果调试系统以及优化性能时,还需要了解API是如何翻译到这两种系统上的。所以现在除非用户一定需要,否则我们不推荐同时使用两者)

So, why the excitement about the Lambda Architecture? I think the reason is because people increasingly need to build complex, low-latency processing systems. What they have at their disposal are two things that don’t quite solve their problem: a scalable high-latency batch system that can process historical data and a low-latency stream processing system that can’t reprocess results. By duct taping these two things together, they can actually build a working solution. In this sense, even though it can be painful, I think the Lambda Architecture solves an important problem that was otherwise generally ignored. But I don’t think this is a new paradigm or the future of big data. It is just a temporary state driven by the current limitation of off-the-shelf tools. I also think there are better alternatives.(lambda架构通过融合现有两种特性迥然不同的框架来提供一个解决方案,但是这种架构并不是大数据的未来,相反只是因为囿于现有两种框架的限制的折衷)

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