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Please welcome our speaker, David Dahl.
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Thank you! Can you hear me? Good. The guy in the top row can hear me.
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So then, everyone can hear me, hopefully. All right, I'm going to talk a bit about JRuby—I know it's a controversial topic.
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To start off, I am a senior developer at a company called Burt in Gothenburg, Sweden. We do analytics for online advertising.
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We primarily use Ruby, and most specifically, JRuby. We manage all of this on AWS.
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That's our case, and that's the story I'm going to share today. Just a brief overview of what we do: we take something like a poorly designed website.
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This particular site is filled with ads, which highlights our goal: to make online advertising a viable option that people don’t hate and that actually works.
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We want to help publishers make money so they can produce good content.
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To achieve this, we first ensure that publishers understand what they are selling.
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We track ads and create insightful graphs. It should be simple, right?
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When we got started, we did what most people do: we logged everything into a database and created reports.
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However, this approach broke down during our first major campaign—no surprise there.
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We realized we needed to pre-calculate everything, which involved a lot of calculations.
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Initially, we had everything in one major application, which made deployment extremely daunting.
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At that point, we were also still using MRI Ruby, which has its own bottlenecks.
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We realized that we needed to change our approach.
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We conceptualized an idea that looked somewhat like this: imagine each dot here represents one application or service.
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Every service performs a specific task, and we send data along a pipeline, refining it through each service.
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Eventually, this process results in useful metrics that we can display in our web applications.
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One critical lesson in building a distributed system is to always start with at least two of everything.
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This helps solve the hard part of the problem.
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Going from one to two services is challenging, but scaling up from two to three or four is much easier.
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As we started implementing this idea, we got stuck.
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Still using MRI, we planned to separate and buffer operations with RabbitMQ, which uses EventMachine.
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We intended to handle storage with MongoDB, but these blocking operations led to issues.
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Ruby's threading limitations meant we couldn't effectively manage concurrent processes.
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After a lot of deliberation, we considered switching to Java.
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Although enterprise solutions often have a bad reputation in our community, they have their merits.
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Enterprise tools are proven and come with many libraries, especially for high-performance applications.
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We soon discovered JRuby, which allows us to utilize Java’s capabilities while writing in Ruby.
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With JRuby, we gain threading, a real garbage collector, and just-in-time compilation.
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We also have access to a vast array of Java, Scala, and Ruby libraries.
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As we delved into wrapping Java libraries, we found it quite enjoyable.
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This experience made coding much more enjoyable.
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So, we proceeded with this direction, but we faced various challenges.
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One major challenge was ensuring that we never experienced downtime.
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We track advertisements, and our processes must remain invisible to visitors.
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If something fails, users typically reload the page, which should not happen with our service.
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We need to continuously receive data. While we can afford latency, we cannot afford to stop receiving data.
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As long as our web server acknowledges receipt with a '200 OK,' we can buffer data and process it later.
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Given that we operate a major application across over a hundred AWS instances, we must avoid unexpected errors.
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It's acceptable for our application to crash occasionally, provided we can restart it and fix any issues in a timely manner.
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However, data can build rapidly in buffers in a short time, so we need to act quickly.
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Buffering became a critical part of our approach.
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We came to really appreciate RabbitMQ, as it was the best architectural choice we made.
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This queuing system facilitated dividing our operations into isolated services.
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We had to carefully consider the interfaces between services and how we would represent data externally.
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Furthermore, when adding a buffering layer, it’s important to consider how transactions will work.
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This involves determining whether to acknowledge messages before or after persisting them.
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If you receive a message and persist data, if an error occurs while persisting, you must decide how to handle it.
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You can either get the message one extra time or lose some data, depending on your acknowledgment strategy.
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Making operations idempotent means that even if you receive duplicates, the operation remains consistent.
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This topic or item potency deserves a separate discussion.
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Regarding databases, we learned the hard way how crucial it is to select the right tools for each job.
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We started using MongoDB everywhere. For those who have heard us discuss it, you know our mixed feelings.
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While MongoDB can be highly effective in the right context, it can also be extremely frustrating in the wrong context.
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We spent weeks troubleshooting when it didn’t fit our needs.
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We also incorporated Cassandra into our database family. It's an impressive yet complex system.
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Cassandra is very Java-centric, which can be a pro or a con, depending on your perspective.
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Other databases we recommend include Redis for certain applications.
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An alternative approach is to pursue a no-database model, keeping everything in-stream without storing it.
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Only keep data in memory until processed.
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Now let’s talk about code and Java. When building distributed systems, Java is a key platform.
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Java's concurrency library provides everything you need. For those looking for a quick guide, I recommend a specific book.
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Executors in Java allow for easy threading and work nicely within Ruby.
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You can submit a block and specify a thread size based on your machine’s capabilities.
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However, be aware that issues can arise, as we experienced with the JRuby interpreter.
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Occasionally, it misinterprets classes, leading to unexpected behavior.
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Despite these hiccups, most time things should work as expected.
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Blocking queues are another great feature in Java's concurrent library.
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They allow for producer-consumer patterns while considering back pressure, which I'll discuss next.
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For example, say you have an application that processes data from a queue and persists it to a database.
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What happens if your persistence thread slows down? If you create an unbounded queue, you could run out of memory.
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This leads to a crash when the queue fills up.
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A better approach involves setting a size limit on the queue, ensuring that the input thread pauses until there is room.
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We've learned this lesson painfully—backpressure can't be ignored.
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When threading, consider atomic variables and concurrent data structures, as shared mutable state is tricky.
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Java provides mechanisms like count down latches and semaphores for distributed locks.
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The Google Guava library is also an excellent resource, addressing gaps in Java’s concurrency offerings.
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It includes various utilities like caches, multi-maps, and more.
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LMAX Disruptor is a high-performance inter-thread messaging library, built for real-time applications.
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It’s an innovative solution to explore for high-performance JRuby applications.
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In summary, managing multithreading in JRuby requires an understanding that thread safety is complex.
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Utilizing Java’s utilities can make life easier; avoid shared mutable state.
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Consider techniques like back pressure in your designs.
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Let’s discuss actors. How many of you have heard of actors?
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Akka is a famous concurrency library in Scala, widely recognized for its actor-based model.
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We've created a small Ruby wrapper called Mika for easier use.
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The library simplifies implementation, though it’s not actively maintained.
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Storm is another ontology-based system that handles processing for you. How many of you have heard of Storm?
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Storm manages the distribution of tasks effectively. It was acquired by Twitter.
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Regarding RabbitMQ and Storm, I personally favor RabbitMQ.
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We utilize a library called Redstorm, which abstracts many difficult aspects of using Storm.
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However, Storm didn’t work for us due to our high branching factor.
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This means that each item fed into the system generated hundreds of operations.
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We needed to wait for all these operations to be persisted before acknowledging them.
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The overhead from this process was inefficient for our needs.
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On the topic of big data, how many of you are familiar with Hadoop?
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My colleague, Theo, developed a library called RubyDupe, which provides a nice abstraction for writing Hadoop jobs.
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You can implement mappers and reducers by defining map or reduce methods.
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Then you set up a job to specify input and output and run it.
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However, managing Hadoop's infrastructure and versions poses various challenges.
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If you're interested in Hadoop, research its staggering versioning issues.
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And just like that, I’ve finished faster than I expected.
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Now I have time for some questions.
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We have also developed small Ruby wrappers for various Java libraries.
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Hot Bunnies is a wrapper for RabbitMQ, now maintained by the same person who oversees the AMQP gem.
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Druidice is a wrapper for Cassandra. My colleagues creatively opted for German names.
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Pillops is another library that wraps 0MQ, and Multimeter is for Yammer Matrix.
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That concludes my presentation.
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Are there any questions?
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Yes, the question is whether JRuby is faster or slower than Java for running Hadoop.
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Overall, JRuby on the JVM is indeed slower than Java.
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However, the difference isn’t significant, and implementing solutions faster can be more valuable.
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We find it more critical to scale horizontally rather than maximize performance.
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For instance, using AWS’s Elastic MapReduce, you pay by the hour.
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While performance is relevant, it isn’t a significant enough issue for us.
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Are there any additional questions?
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When using RabbitMQ as a buffer, do we maintain persistence?
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Yes, we persist everything to ensure reliability. Otherwise, we would risk data loss if the system fails.
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RabbitMQ has improved significantly, addressing prior back pressure issues.
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In earlier versions, if pushed too fast, you would encounter performance problems.
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Is RabbitMQ used for inter-process communication?
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Yes, we utilize it as an alternative to HTTP for communication between nodes.
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Thank you!
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Thank you all!
