Monday, 30 March 2015

ChronicleMap - Java Architecture using Off Heap Memory

My last post was written a couple of weeks ago and after some valid feedback I'd like to clarify a couple of points as a preface to this article.

The main takeaway from 'Creating millions of objects with Zero Garbage' should be that with Chronicle you are not 'limited' to using jvm allocated on-heap memory when writing a Java program. Maybe the article would have been more aptly titled 'Creating Millions of Objects using Zero Heap'. Another point I wanted to bring out was that when you have no heap memory you cause no GC activity. 

A source of confusion came from the fact I used the term 'garbage' to describe the objects allocated on the heap. The objects allocated were actually not garbage though they caused GC activity. 

I contrived an example to demonstrate, one, that ChronicleMap does not use heap memory whilst ConcurrentHashMap does, and two, that when you use heap memory you can't ignore the GC. At the very least you need to tune your system carefully to ensure that you don't end up suffering from long GC pauses. This does not mean that there are no issues with allocating from off heap (see the end of this post) and it also does not mean that you can't tune your way through an on heap solution to eliminate GC. Going off heap is by no means a panacea to all Java performance issues but for very specific solutions it can deliver interesting opportunities some of which I will discuss in this post.

Let's examine this problem:

You have multiple JVMs on your machine and need to share data between them. You would also like that data to be persisted so that when the JVMs exits the data does not disappear.

Let's simplify for now and say that you have two JVMs running on the same machine, either or both of which would like to see updates from the other. Each Java program has a ConcurrentHashMap which it updates, those updates are stored and are of course available to it later. But how does the program get the updates applied by the other Java program to its map? And how do we prevent the data from evaporating when the programs exit?

Fundamentally, JDK on-heap collections such as HashMap and ConcurrentHashMap can't be shared directly between JVMs.  This is because heap memory is contained by the JVM through which it was allocated. Additionally when the JVM exits, the memory is released and the data is no longer available, there is no implicit way of persisting the memory outside the lifetime of the JVM. So you need to find some other mechanism to share the data between the JVMs and persist the data.  

From an architectural perspective you need accomplish these two tasks.
  1. A mechanism for sharing the data between the JVMs so that when one process updates the other will be informed of the action.
  2. A mechanism for storing the data so that when one or both JVMs exit the data does not just disappear.
Typically you might use a database as an external sharable store and messaging service to send the data updates to other processes to notify them that some data has been updated.

This results in the following architecture:

The problem with this architecture is that use lose the in-memory speeds of a HashMap, especially if writing to your database is not that fast and you want the write to be persisted before you send the message out over the messaging service. Also many solutions will involve TCP calls which can again be a source of latency. There are of course much faster ways to persist data than writing to a fully fledged database using mechanisms like journaling to disk, for example using a product like ChronicleQueue or similar.  But if you did use a journal you'd still have to build all the logic to recreate a Map data structure on restart not to mention having to keep a Map type structure up-to-date on another JVM.  In addition to the latency introduced by this architecture there is the complication of having to deal with the extra code and configuration for the database and messaging service. 

Even accepting that this sort of functionality can be wrapped up in frameworks, wouldn't it be great if your in memory Map was actually visible outside your JVM.  The Map should be able to implicitly persist the data so that its data is available independently of the life time of the JVM. It should allow access with the same 'memory' speeds as you might achieve using an on heap Map.

This is where ChronicleMap comes in.  ChronicleMap is an implementation of java.util.ConcurrentMap but critically it uses off heap memory which is visible outside the JVM to any other process running on the machine. (For a discussion about on-heap vs off-heap memory see here). 

Each JVM will create a ChronicleMap pointing at the same memory mapped files. When one process writes into its ChronicleMap the other process can instantly (~40 nanoseconds) see the update in its ChronicleMap. Since the data is stored in memory outside the JVM, a JVM exit will not cause any data to be lost.  The data will be held in memory (assuming there was no need for it to be paged out) and when the JVM restarts it can map it back in extremely quickly.  The only way data can be lost is if the OS crashes whilst it has dirty pages that haven't been persisted to disk. The solution to this is use replication which Chronicle supports but is beyond the scope of this post.

The architecture for this is simply this:

For a code example to get started with ChronicleMap see my last post or see the official ChronicleMap tutorial here.

There are a number of caveats and trade-offs to consider before diving into ChronicleMap.
  • The ChronicleMap entries have to be Serializable.  For systems that are very sensitive to performance you will need to implement the custom serialisation provided by Chronicle known as BytesMarshallable. Whilst this is pretty easy to implement it is not something that is necessary with an on-heap map. (Having said that storing data into a database will of course also require some method of serialisation.) 
  • Even with BytesMarshallable serialisation, the overhead of any serialisation might be significant to some systems. In such a scenario it is possible to employ a zero copy technique supported by Chronicle (see my last blog post for more details) to minimise the costs of serialisation. It is however a little trickier to implement than using 'normal' Java.  On the other hand in latency sensitive programs it will have the huge benefit of not creating any objects that might then later need to be cleaned up by the GC.
  • A ChronicleMap does not resize and must therefore be sized up front. This might be an issue if you have no idea how many items to expect.  It should be noted however, that oversizing, at least on Linux, is not a huge problem as Linux passively allocates memory. 
  • Chronicle relies on the OS to asynchronously flush to disk. If you want to be absolutely sure that data has actually been written to disk (as opposed to just being held in memory) you will need to replicate to another machine. In truth any mission critical system should be replicating to another machine so this might not be a big issue in adopting Chronicle.
  • ChronicleMap will be subject to OS memory paging issues. If memory is paged out and has to be swapped back in latency will be introduced into the system. Therefore even though you will be able to create ChronicleMaps with sizes well in excess of main memory, you will have to be aware that paging might occur depending on your access patterns on the data. 


  1. Thanks for the article.It is useful.

  2. Technical courses of bachelor in architecture and masters in architecture are the usual degrees that are on offer to be studied.

  3. Watching your favorite movies and tv shows have become so easy these days, thanks to some great apps like ShowBox. It allows you to watch movies in multiple resolutions according to your preference and it is absolutely free as well.
    Just check out my site to know how to install ShowBox on your smartphones
    ShowBox for PC

  4. Technical courses of bachelor in architecture and masters in architecture are the usual degrees that are on offer to be studied.
    Lucky Patcher
    teclast t10

  5. pleasant post, stay aware of this fascinating work. It truly regards realize that this subject is being secured likewise on this site so cheers for setting aside time to talk about this!

  6. The reasoning and rationale behind this blogs makes it a brilliant read.
    go to my site

  7. Why do only so much written on this subject? Here you see more.
    clicking here

  8. GBWhatsapp apk Download Latest Version 2018. Download Latest GB Whatsapp for Use 2 Whatsapp in One Mobile.  GBWhatsApp APK

  9. Use dual account with GBwhatsapp Latest Application With free of cost. Gbwhatsapp

  10. Gbwhatsapp is Best app for using two accounts on one mobile.

    Gbwhatsapp APK

    Yowhatsapp APK

    whatsapp plus Apk

  11. Download Morpheus TV App and watch all movies and shows with great quality.

  12. Even accepting that this sort of functionality can be wrapped up in frameworks, wouldn't it be great if your in memory Map was actually visible outside your JVM. The Map should be able to implicitly persist the data so that its data is available independently of the life time of the JVM. It should allow access with the same 'memory' speeds as you might achieve using an on heap Map. GBWhatsapp APK Download Latest Version

  13. I am looking for and I love to post a comment that "The content of your post is awesome" Great work!
    Hardwood Flooring

  14. Gbwhatsapp is the best modded app of popular application nowadays. I am very confident to say you will like this app, because its have many features.


  15. We all know about the app GBWhatsApp which is the most popular among all mods of whatsapp. It is unofficial also but there is a lot of features in this app that made people crazy. Today with the new technology people want advance technology in modern era that’s why people attracted more with mods of apps then official. As we know that there are many mods of whatsapp available but GBWhatsApp is the best in all of these.for more Updates Visit Our GBWhatsApp APK

  16. I simply want to tell you that I am new to weblog and definitely liked this blog site. Very likely I’m going to bookmark your blog . You absolutely have wonderful stories. Cheers for sharing with us your blog. off page seo


  17. Excellent Blog! I would like to thank for the efforts you have made in writing this post. I am hoping the same best work from you in the future as well.
    I wanted to thank you for this websites! Thanks for sharing. Great websites!

    Pubg APK
    Pubg Mobile APK
    Pubg Download
    Download Pubg Mobile
    Pubg Mobile Download

  18. This comment has been removed by the author.

  19. All The Interested Candidates Read The Notification of The Following Vacancy. Read and Check Are You Eligible For This Vacancy and Read The How to Apply The Online Form of This Job. Online Quran teacher.

  20. Optimization of websites is a very important strategy to deliver the best results. SEO or search engine optimization using the best proven strategies helps to make business websites appealing to search engines. ralevant backlink

  21. Similarly, some SEO service providers provide services that are more comprehensive in a much more professional manner customized according to the client thereby leading to a low number of clients. seo

  22. If you want to use backlinks to your best interest, edu blogs are effective. Using this opportunity correctly, you will be able to increase traffic to your site. off page seo
    The tip that professionals use is the promise to find those which are 'do follows' and benefit SEO pages. niche ralevant blogcomment

  23. My heartiest congrats to the author on composing this.
    southend roofing

  24. Lovely visit of this website where I am letting about delicious recipe of making pumpkin cupcakes.
    Like to bookmarking this website and surly visit again. Keep posting.

    WOF Wheel of fortune answer

  25. Excellent Blog.Thank you for sharing this amazing info. If you want to download videos from YouTube then I recommend you download tubemate 2019 app here you can easily download any videos you were like.

    Download TubeMate 2019 APK

  26. unity game development company
    ui ux design company usa
    ios game development company
    mobile game development company usa
    ui ux design services company
    digital marketing services usa
    best custom software development
    digital marketing company in usa
    ui ux design agency
    ios app development company
    game development company
    Underground Studio is a leading Unity 3D Mobile games Development Company based in the USA that offers Unity 3D games development, IOS app development by expert Unity 3D games developer with the best software developers to provide custom software development for companies of all sizes.

  27. thanks for sharing this great about java. keep it up.
    Apental calc app. It is a wonderful app that lets you get hundreds of followers on Facebook for free. The application work to promote your Facebook account by providing likes and comments on your post. Download it now.
    apental calc
    wefbee apk latest version

  28. Most of the time I don’t make comments on websites, but I'd like to say that this article really forced me to do so. Really nice post! 62 niche related backlink blog comment

  29. Even after you get into the top position, you will have to continue your SEO backlink creation so that you are able to maintain that rank and have a consistent flow of traffic. Seo backlinks

  30. Thanks a lot for sharing us about this update. Hope you will not get tired on making posts as informative as this. off page seo

  31. that soon only the rich and super rich will be able to afford even those items considered necessities, it is wise to save and get out of debt right now. triple twin bunk bed

  32. If you are interested in business directory or want database marketing. We also provide sales automation and marketing automation tools. If you are interested, then please contact us for detailed information.


  33. Some of the most successful ABS-CBN programs from the 1990s up to the present
    bear his imprint — from “Showbiz Lingo”, “The Buzz”, lambingan - Watch your favorite Pinoy Tambayan, Pinoy Teleserye Replay, Pinoy
    TV Series and Pinoy TV Shows online for free! “Today With Kris”, “Game Ka Na Ba?”, “Mula
    Sa Puso”, “ASAP” and recent hits “May Bukas Pa”, “Tayong Dalawa”, “Walang Hanggan” and “Ang Probinsyano”.

  34. gogo anime Watch anime online in English. You can watch free series and movies online and English subtitles.

    lottery sambad 2020  is the Indian lottery system. The important and main thing which attracts the people to invest in this lottery is the number of prizes and size of the lottery. There are many other lotteries in India but sambad is a very popular lottery among the Indian people.


  35. In each dialogue box, the movies chronologically segregated in descending order.
    This site is very organized and very possible. The film can be searched alphabetically.
    From 0-9 and the alphabets individually can be searched.Hollywood, Bollywood, Malayalam, Tamil
    and Telugu movies. Once you open the website, you will be able to see a range of options.123Movies,
    GoMovies, GoStream, MeMovies or 123movieshub,movierulz,hindi movies,Bollywood | Hollywood | Songs | Punjabi
    | Hindi Dubbed | Songs | Hindi Webseries Season | Netfilix | ULLU App

    In a separate dialogue box, we can search by the plethora of the genres provided to us. Action, animation, adventure,
    biography, comedy, crime, documentary, drama, family, fantasy, film-noir, game show, history, horror, music, musical, mystery,
    news, reality show, romance, sci-fi, sports, talk- show, thriller, war and western and various genres can be found here.

  36. Watch 9anime online in high quality for free with English subbed, dubbed. Update daily, No tracking, No paying, No registration required. Just enjoy your anime

  37. Great, your post is helping me a lot. Thanks for the detailed info on this topic. It’s hard to find nowadays to know about the basics but you did it so much well. I would love to see more about FM Whatsapp APK. Keep sharing and updated. Also share more posts with us. Thank you.

  38. Hey! I just wanna say that you are sharing a quality and useful content with us. This kind of content is difficult to find it and you are sharing FMWhatsApp is very good. Keep up the high work.

  39. Thanks for sharing this very use full information. Also check Download GBWhatsApp APK

  40. Thank you for sharing this. It was helpful. Keep sharing such things.
    Also I like to play COC MOD Apk which is more fun than any other game.

  41. Thank you for sharing this. It was helpful. Keep sharing such things.
    Also I like to play.SolidWorks Premium

  42. This was an excellent article. Thank you for sharing it.
    Xilisoft Video Splitter

  43. I was looking for Java Architecture using Off Heap Memory. thank you for the complete information. COC Mod APK


  44. Wow! very beautiful, great, and good post. I like it very much.

  45. Many thanks for the shared this informative and interesting post with me.Driver Talent Pro

  46. I wanted to thank you for this great read!! I definitely enjoying every little bit of it I have you bookmarked to check out new stuff you post.
    Microsoft Office 2007

  47. A good blog always brings new and exciting information, and as I read, I feel that this blog really has all those qualities that qualify a blog to be one.
    Product Key for Microsoft Office 2007

  48. That's an outstanding piece of work!I look forward to seeing more!
    mirillis patch

  49. I wanted to thank you for this great read!! I definitely enjoying every little bit of it I have you bookmarked to check out new stuff you post.

  50. Really very nice information on this site. Thanks for sharing this nice information. I hope you'll continue to write like this in the future.
    SAM BroadCaster


  51. I hope this post is beneficial for viewers. Many thanks for the shared this informative and interesting post with us.

  52. All issues have been explained clearly and openly. I certainly found the presentation informative. I appreciate your site.
    Many thanks for the shared this informative and interesting post with us

    Revo Uninstaller Pro

  53. Thanks for the detailed article on this topic. I would like to see more such awesome articles from you. Also you can get the new and best features of FMWhatsapp which are coming in 2022-

    FMWhatsapp APK

    1. Yes brother FMWhatsapp is more better than the original, I'm also using it. Thank you!

  54. You explained & solved this question very clearly. It was so easy to get through this blog. Thank you. fmwhatsapp

  55. That is one of the most crucial pieces of information for me. And I've enjoyed reading your article.
    However, I'd like to make a few general remarks: The website's design is fantastic, and the posts are truly good : D.
    Best of luck with your endeavours.
    bulk image downloader crack
    netbalancer activation code download
    nero burning rom crack
    ntlite license key latest version


  56. Your post style is super Awesome and unique from others I am visiting the page I like your style.
    Website Ripper Copier

  57. You write in such an amazing style and I really enjoy visiting your website. I hope you'll continue to write like this in the future. adobe muse crack

  58. I like your post very much it is very informative and interesting. Your posts always inspire me. Keep sharing such wonderful posts, it motivates a lot. windowsmoviemaker

  59. Many thanks for the shared this informative and interesting post with me.

  60. Hi Dear, I like your post style as it’s unique from the others. I’m seeing on the page.
    Neural DSP Fortin Nameless Suite


  61. Most of the people who have used this software around the world love works of art. This software was released 29 years ago. It is the most powerful, innovative and creative feature that professionals need. Powerful design software built for photographers and artists. GTA Vice City Highly compressed Ispoofer Crack boris fx license key crack wondershare mobiletrans cracked Alien skin blow up Crack Best Korean Action Movies macdrive Pro ZModeler Free macdrive Pro snapgene license keysoftware is essentially designed for graphic designers. Adobe Photoshop CC is photo editing software designed for professionals and artist-designers. This software has a creative cloud service and creative tools to enhance your images. About this software, we provide information on the fact that it has many cutting-edge features and also get into learning applications with the learning panel.

  62. Hi Dear, I like your post style as it’s unique from the others. I’m seeing on the page.

  63. It is really enjoyable to visit your website because you have such an amazing writing style.
    Neural Fortin Nameless Crack


  64. I am very impressed with your post because this post is very beneficial for me and provide a new knowledge to me.
    4Front TruePianos Crack

  65. Yes you heard it right I almost used every WhatsApp mod and checked all mods themes features and I found Amazing themes those are better than other WhatsApp Mods in FMWhatsApp.

  66. Your Blog is awesome. Really Admire your work!
    Veeam Backup & Replication Activation Key is amazing software for professional and personal use. Thanks to its simple and intuitive interface, anyone can use it with little knowledge.
    I can say that this software did not disappoint you at all. Anyone can download and use it for free.

  67. I like your all post. You have done really good work. Thank you for the information you provide, it helped me a lot. I hope to have many more entries or so from you.
    Very interesting blog. Crack
    MacDrive Crack
    ShieldApps Webcam Blocker Premium Crack
    VyprVPN Crack

  68. Hi dear,It is really enjoyable to visit your website because you have such an amazing writing style.
    Minitool Partition Wizard Crack

  69. I guess I am the only one who came here to share my very own experience. Guess what!? I am using my laptop for almost the past 2 years, but I had no idea of solving some basic issues. I do not know how to Download Crack PC Softwares But thankfully, I recently visited a website named Crackroom
    MacDrive Pro Crack

  70. I like your all post. You have done really good work. Thank you for the information you provide, it helped me a lot. I hope to have many more entries or so from you.
    Very interesting blog.(
    Macdrive Pro Crack
    Acronis True Image Crack
    Loaris Trojan Remover Crack
    Alien Skin Blow Up Crack
    McAfee LiveSafe Crack

  71. This is very useful information. I admire your efforts. I found your expertise to be quite useful, and I appreciate you sharing it with me. I'd like to see a lot more of your work.

  72. I must say it is very informative as well as interesting. Thanks to the author of this post/page for writing such wonderful lines. abelssoft-filefusion-crack/

  73. Check these websites
    1= Check out my website for the variety of paid APKS for free
    Iphone side

    2= Check this for latest TV shows update

    3= Check this for Wedding Ideas
    Wedding Articles

    4= Check this for Dramas
    GEO TV
    HUM TV

  74. MY BLOG support of this software, users no longer have to register on several MY LINK websites at exactly the same time to control investments, and they don’t have to think about a large number of passwords that keep theirwebsite information safe. With the entire program, customers can quickly access their savings, credit card information, investments, loans or retirement accounts, all from one place. Website My

  75. I am very happy to read this article. Thanks for giving us Amazing info. Fantastic post.
    Thanks For Sharing such an informative article, Im taking your feed also, Thanks.outotec-hsc-chemistry-crack/

  76. The Formation of content is very good, a great example of writing skills. Thank you for sharing.You can also check mine Renee PassNow Pro Crack