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Garbage Collection - The Useful Parts

*Please note this is an LJC event. Skills Matter are hosting this event and are handling the attendance - it is essential that you confirm your place at this link: *

Presented by Martijn Verburg and John Oliver: Garbage Collection - The Useful Parts

This presentation will give the busy Java/JVM developer an overview of how Garbage Collection in the JVM works and the common collectors that are used. We'll also cover how to read and interpret the scary log format and most importantly, offer strategies to deal with badly behaving memory (e.g. The dreaded OOME!).

Who Should Attend:

Any Java or JVM language developer who wants to learn about the deep dark secrets of the GC sub system.


Martijn Verburg: Martijn has over 12 years experience as a technology professional and OSS mentor in a variety of environments from start-ups to large enterprises.

Some career highlights include overhauling technology stacks and SDLC practices at major IBs, mentoring large vendors on technical community management, and running large distributed development teams at a variety of organisations.

He is the co-leader of the London Java Community (over 2800 developers) and leads the global effort for the Java User Group "Adopt a JSR" and "Adopt OpenJDK" programmes.

Martijn's book "The Well-Grounded Java Developer" (with Ben Evans) was published by Manning in 2012.

As a leading expert on technical team optimisation, his talks and presentations are in high demand by major conferences (JavaOne, Devoxx, OSCON, FOSDEM, QCon, etc). Often you'll find him challenging the industry status quo in his alter ego "The Diabolical Developer".

Martijn holds a BSc in Computer Science and a BCA in Information Systems from Victoria University of Wellington.

John Oliver: John is a keen developer and Matlab guru.

John has performed research and development in many languages for 15 years, on various platforms from micro controllers, robots, simulations, desktop applications and web services. He has previously worked on static analysis tools and is particularly interested in reducing our reliance on the relatively blunt and time consuming tools such as unit testing. John also has a special ability to make our continuous deployment chain just work.

He delivers all sorts of interesting analysis on our raw data, and is interested in bringing signal processing and machine learning techniques to analysing performance problems...despite us endlessly needling him about his love for Matlab.

John holds a PhD in Engineering from Warwick University working on algorithms for coordinating mobile robotic teams. During his study he performed extensive work on both physical and simulated robotic platforms.


18:00/18:30: Doors Open
18:30 Martijn Verburg and John Oliver will present "Garbage Collection - The Useful Parts"
20:00/20:30: Networking

Please Note:

Nearest tube: Barbican
Nearest Coffee Shop: Sun Coffee Shop, 55-63 Goswell Road, London, EC1V 7EN for if you arrive early
For after event drinks: The White Lion, 37 Central Street, City Road, London, EC1V 8AB

*Please note this is an LJC event. Skills Matter are hosting this event and are handling the attendance - it is essential that you confirm your place at this link: *

Event Organised by RecWorks

Join or login to comment.

  • Barry C.

    Hey guys, Something you may be interested in based around low level programming. We are organising an event with a recruitment focus for the evening of Tuesday 23rd April. It will be an exclusive networking/recruitment event targeted at projects involving low level core Java, (concurrency, multithreading etc). We will have developers from 3-4 employers and 20-30 attendees. If you are interested in coming along or finding out more about the event please do let me know on [masked]

    April 11, 2013

  • Michal A.

    Many thanks for sharing that!

    February 8, 2013

    • Martijn V.

      Ben's GitHub JavaFX project has an uptodate version

      February 8, 2013

    • Mani

      Thanks Martijn, Here's the link to Ben's github repo:­

      February 8, 2013

  • Irfan

    It was really informative session and hope this would cover more in next presentation about why PermGen space was introduced and garbage collecting the objects with weak references. Learned from Martin that some time specification is ignored by the implementor for example when you invoke System.gc(), specification says it requests to JVM for GC and its up to JVM to honour it, but most of the implementation actually do run the GC, something new for me :-). Looking forward for next talk

    January 18, 2013

    • Martijn V.

      Hi Irfan, PermGen was introduced as the JVM itself has classes that need to be permanently live. Since they'll never be garbage collected it was a good idea to store them somewhere safe out of the way as it were. Over time more applications and servers etc have added extra classes that 'always need to be live' so the size of permgen has needed to be increased (often by developers who get the dreaded OOME PermGenSpace message). Yes the System.gc() urban myth is an interesting one. We have yet to see an implementation which doesn't actually honour the agreement, however the specification says that it doesn't have to honour the agreement so one day the implementation may match that spec.... :-)

      January 18, 2013

  • Martijn V.

    Hi all,

    Thanks for coming along last night - it was a great crowd and I'm glad the information was useful to many of you. We do intend on following up with another presentation that will be purely tuning demonstration. It will naturally assume good basic knowledge on the part of the audience though!

    If you really want to dive into the theory and details some more then please join our friends of jClarity programme - we have a fun list of about ~250 performance and JVM geeks discussing this sort of thing daily :-). See for the signup details

    Also don't forget to signup for Devoxx UK in March - - this conference is pretty much by the LJC for the LJC and will feature many presentations of a similar vein to last nights.

    Thanks again,

    1 · January 18, 2013

  • Fahd

    Really informative

    January 18, 2013

  • David G.

    I thought this was a very useful talk which gave a good introduction to some of the basic theory behind garbage collection. I am looking forward to the next presentation that will cover more practical aspects of tuning and measuring the impacts of these changes.

    3 · January 18, 2013

  • wojciechjanus

    It would be nice to have a bit more details.

    January 18, 2013

  • Vijay B.


    January 17, 2013

  • Martijn V.

    Hi Craig, thanks for the spot - this is fixed

    January 14, 2013

  • Craig S.

    I think the skills matter signup page link is wrong. Does anyone have the correct link as I'm struggling to find it on the skills matter site?

    January 14, 2013

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