GoTo Con AMS - Day 1
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Last week GoTo Con took place in Amsterdam. Being a sister conference to GoTo in Aarhus the Amsterdam event focused on the broad topics of agile development, architectural challenges, backend and frontend development, platforms like the JVM and .NET. In addition the Amsterdam event featured a special Apache track tailored towards presentations focusing on the development model at Apache and the technologies developed at Apache.
So far Dart is just a tech preview - on the agenda of the development team we find items such as better support for REST arguments, enums, reflection, pattern matching, tooling for test coverage and profiling. All code is freely available, also the language specification and tutorials are open. The developers would love to get more feedback from external teams.
Twitter JVM tuning best practices
In his presentation on JVM tuning Attila Szegedi went into quite some detail on what kind of measures Twitter usually takes when it comes to optimizing code that run on the JVM and exhibits performance issues. Broadly speaking there are three dimensions along which the usual culprits for bad performance hide:
- Memory footprint of the applciation.
- Latency of requests.
- Thread coordination issues.
Memory footprint reduction
A first step always should be to verify that memory is actually responsible for the issues seen. Running the JVM with verbosegc turned on helps identify how often and how effective full GC cycles happen on the machine. Next step is to take into account the simple solution: Evaluate whether the application can simply be given more memory. If that does not help or is impossible start thinking about how to shrink memory requirements: Use caching to avoid having to load all data im memory at once, trim down the data representation used in your implementation, when looking into what to trim know exactly what amount of memory various objects need and how many of these object you actually keep in memory - this analysis should also go into detail when using code generated from frameworks like thrift.
When taking a simple view latency optimization boils down to making a tradeoff between memory usage and time. A little less naive view is to understand that actually it is a set of three goals to optimize:
Tuning an application means to take the product of the three, shift focus but keep the product stable. Optimization is assumed to increase the resulting product.
Biggest thread to latency are full gc cycles. Things to keep in mind when tuning and optimizing: Though the type of gc to run is configurable, this configuration does not apply to cleanup of eden space - Eden is always cleaned up with a stop-the-world gc. In general this is not too grave, as cleaning up objects that are no longer referenced is very cheap. However it can turn into a problem when there are too many surviving objects.
When it comes to selecting GC implementations: Optimize for throughput by delaying GC for as long as possible. This is especially handy for bulk jobs. When optimizing for responsiveness use low pause collectors - they incur a somewhat constant penalty however those avoid having single requests with extremely large response time. This is most handy for online jobs.
Other options to look into: Use adaptivesizepolicy and maxgcholdmillis to allow the jvm to size heap on its own based on your target characteristics. Use the printheapatgc option to view gc heap collection statistics - especially watch out for fromspace being less than 100%, use printtenuredistribution to keep an eye on number of ages, size distribution. In general, give an app as much memory as possible - when using concurrent mark and sweep implementation make sure to over-provision by about 25 to 30% to give the app a gc cushion for operation. If you can spare one cpu, set initiateoccupationfraction to 0 and let gc run all the time.
The last issue in general causing delays are thread coordination issues. The facilities for multi-threaded programming in Java are still pretty low level - even worse, developers generally hardly know about synchronized - not so much about the atomic data types that are available - let alone other features of the concurrent package.
Make sure you check out the speaker's slides they certainly contain valuable information for developers that want to scale their Java applications.
Another talk that was pretty interesting to me was the introduction of Akka - a project I had only heard about before but did not have any deep technical background knowledge on. The goals when building it were fault tolerance, scalability and concurrency. Basically an easy way to scale up and out. Built in Scala, Akka also comes with Java bindings.
Akka is built around the actor model for easier distribution. Actors are isolated, communicate only via messages and have no shared memory - making it easy to run them in a distributed way without having to worry about synchronization. Distribution across machines is currently based on protocol buffers and NIO. However the resulting network topology is still hard wired during development time.
The goal of new Akka developments is to make roll-out dynamic and adaptive. For that they came up with a zookeeper based virtual address resolution, configurable load balancing strategies and the option for reconfiguration during runtime.
The first day was filled with lots of technical talks - so several remained more on the overview/introductory level - which is a good thing to learn about new technologies. In addition there were a few presentations on new features of upcoming and past releases for instance for Java 7 and Sprint 3.1 - it's always nice to learn about the rational behind changes and improvements.
As for the agile talks - most of them propagated pretty innovative ideas that need a lot of courage to put into practice. However in several cases I could not help but get the feeling that either the processes presented were very specific to the environment they were established in and would not survive sudden stress - be it decline in revenue or team issues. In addition quite a few ideas that were introduced as novelties were already inherent in existing processes: Trust and natural communication really is the goal when establishing things like Scrum. In the end, the meetings are just the tool to get there. Clarity wrt to vision and even business value is core to prioritizing work to be done. Understanding and finding suitable metrics to measure and monitor business value of a product should be at the heart of any development project.
Overall the first day brought together a good crowd of talented people exchanging interesting ideas, news on current projects and technical details of battle-field-stories. Being still rather small, the Amsterdam edition of GoTo con certainly made it easy to get in touch with speakers as well as other attendees over a cup of coffee and discuss the presented issues. Huge thanks to the organizers for putting together an interesting schedule, booking a really tasty meal and having a friendly answer to any question from confused attendees.