Heapoff memory wtf
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This document discusses reducing heap memory stress in Java applications by using "heap-off memory" techniques. It provides an overview of Java memory fundamentals and the limitations of on-heap caching. It then introduces Apache DirectMemory as an open source project that implements an off-heap caching solution using ByteBuffers to improve performance by reducing garbage collection overhead. Examples of using DirectMemory for multi-layer caching and as a cache server are also presented.
![Heap Off Memory
How to use that ?
You can manipulate only Buffer (ByteBuffer byte[]
etc..) !
So you must serialize/deserialize your datas
Maximum size with -XX:MaxDirectMemorySize=](https://image.slidesharecdn.com/heapoff-wtf-120614021540-phpapp02/85/Heapoff-memory-wtf-9-320.jpg)
Heapoff memory wtf
- 1. Heap Off Memory WTF ?? Reducing Heap memory stress
- 2. Abstract * Java memory fundamental * heap off memory principles * heap-off cache with Apache DirectMemory
- 3. /me Olivier Lamy * Open Source Architect @Talend Apache Team * Apache Member : Maven, Archiva, Tomcat, DirectMemory, Build Infra, etc.. * Jenkins * Add bugs in various OpenSource projects * twitter.com/olamy olamy.blogspot.com
- 5. Java Memory Fundamental The cool part * Automatic memory allocation (do you remember when you used malloc) * Garbage collector (GC) (no more free)
- 6. Java Memory Fundamental The bad part * stop-the-world mode * proportionnal to memory's size * unpredictable unresponsive application : complicated with tight SLA
- 7. Heap Off Memory Not in the Heap process Limited GC stop « Unlimited storage »
- 8. Heap Off Memory How to use that ? Native libraries with JNA https://github.com/twall/jna ByteBuffer @since 1.4 with nio ByteBuffer.allocate( size ) (not off heap) ByteBuffer.allocateDirect( size ) You can use sun.misc.Unsafe but can cause issue and not portable
- 9. Heap Off Memory How to use that ? You can manipulate only Buffer (ByteBuffer byte[] etc..) ! So you must serialize/deserialize your datas Maximum size with -XX:MaxDirectMemorySize=
- 10. Our use case : Cache RAM : 10-60 ns Network : 10000-30000 ns SSD Disk : 70000-120000 ns Disk : 3000000-10000000 ns Cache must use memory !
- 11. On-Heap Cache Objects stored by reference (no de/serialisation) GC storm effect when refreshing/removing objects!
- 12. Off-Heap Cache de/serialisation overhead (hopefully some very performant libraries exist for that) Cache objects payload no more affecting GC
- 13. Solutions : * Terracotta BigMemory (off-heap storage on top of ehcache) * Infinispan (by Jboss) * Huge collections * Apache DirectMemory
- 14. Apache Direct Memory Goals : Apache Direct Memory is a multi layered cache implementation featuring off-heap memory storage to enable caching of java objects without degrading jvm performance.
- 15. Apache Direct Memory Joined Apache Incubator end 2011 12 developpers ATM Under development : Memory allocation service just rewrite APIs are subject to be changed and bugs to be found !
- 16. Design & principles ByteBuffer.allocateDirect is the foundation of the cache ByteBuffers are allocated in big chunk and splitted for internal use
- 17. Design & principles Build on layers CachingService : serialize object (pluggable) MemoryManagerService: Compute ByteBuffer access ByteBufferAllocatorService: Eventually deals with ByteBuffer
- 18. ByteBuffers Allocation Merging Strategy No memory wasted Suffers from fragmentation Need synchronization at de/allocation Fixed Size buffers allocation Memory wasted if size not correctly configured No fragmentation
- 19. Use case (1) Multi layers cache Most used objects are cached on heap, the rest off-heap (maybe overflow to disk) Sounds like ehcache with BigMemory Hard coded class to use : net.sf.ehcache.store.offheap.OffHeapStore So same package class name in Apache DirectMemory (https://jira.terracotta.org/jira/browse/EHC-940) Demo
- 20. Use case (2) Cache Server « à la » memcache tru http(s) But with a REST Api and written in Java Client API available Demo
- 21. > PUT /dm/cache/bordeaux HTTP/1.1 > Content-Type:text/plain {"millesime":"2003","description":"so good so good"} < HTTP/1.1 200 OK < X-DirectMemory-SerializeSize: 58 < Content-Length: 0 > GET /dm/cache/bordeaux HTTP/1.1 > Accept:text/plain < HTTP/1.1 200 OK < Content-Type: text/plain < Content-Length: 51 {"millesime":"2003","description":"so good so good"} > DELETE /dm/cache/foo HTTP/1.1
- 22. Next Steps JSR 107 ? Benchmarks Components Integration (Cassandra, Tomcat etc..) Dynamic cache size modification Management/Monitoring
- 23. Links http://incubator.apache.org/directmemory/ https://issues.apache.org/jira/browse/DIRECTMEMORY Demo project : https://bitbucket.org/olamy/heap-off-memory- wtf Slides : http://www.slideshare.net/olamy