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![OPTIONS FOR OFF-HEAP STORAGE (1/3)
JNI (Java Native Interface)
int*buffer=(int*)malloc(1024* sizeof(int));
if(buffer==NULL)throwOutOfMemoryException();
for(inti=0;i<1024;i++)
buffer[sizeof(int)*i]=i;
free(buffer);
www.hazelcast.com](https://image.slidesharecdn.com/myoldfriendmalloc-131101123327-phpapp02/85/My-Old-Friend-Malloc-19-320.jpg)
Uploaded byChristoph Engelbert
My Old Friend Malloc
The document provides an overview of off-heap memory management in Java, discussing its definition, advantages, disadvantages, and various storage options. It highlights how off-heap memory can help with performance by reducing garbage collection pressure and enabling storage of large datasets. Additionally, the document outlines different frameworks available for managing off-heap storage, such as Apache DirectMemory and Hazelcast, along with a proposal for handling off-heap memory in Java.
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My Old Friend Malloc
- 1.
- 2. WHO AM I ChristophEngelbert(@noctarius2k) 8+ years of professionalJavadevelopment Specialized to performance, GC, traffic topics Apache DirectMemoryPMC Previous companies incl. Ubisoftand HRS OfficialInhabitantof Hazelcastia CastMapRMapReduce for Hazelcast3 Co-Author JavaOff-heap JEP Proposal www.hazelcast.com
- 3. TOPICS JavaMemoryLayout Definition of Off-Heap? DirectMemoryAccess? Whydowe need Off-Heap Memory? Options for Off-Heap Storage Advantages and Disadvantages of (Off- )Heap Available Frameworks (Notso) SecretFuture Smalldemonstration www.hazelcast.com
- 4. JAVA MEMORY LAYOUT AFAST WALK-THROUGH www.hazelcast.com
- 5. JAVA MEMORY LAYOUT(1/5) www.hazelcast.com
- 6. JAVA MEMORY LAYOUT(2/5) YOUNG GENERATION - EDEN SPACE Onlyused for Object-Allocation TLAB¹ allocation available Affected byMinor and Major GC Objects moved to Survivor on Minor GC ¹TLAB:ThreadLocalAllocationBuffer www.hazelcast.com
- 7. JAVA MEMORY LAYOUT(3/5) YOUNG GENERATION - SURVIVOR SPACES Always one From-Space and one To-Space From-Space contains livingobjects on lastGC Minor GC switches the Survivor Spaces Alive Objects are moved to To-Space Affected byMinor and Major GC Longlivingobjects eventuallymoved to Tenured www.hazelcast.com
- 8. JAVA MEMORY LAYOUT(4/5) TENURED SPACE Contains onlylonglivingobjects Affected onlybyMajor GC More objects means more GC spend time Concurrentobjectinspectation available LongStop-The-World pauses possible Notoptimalfor bigdatasets www.hazelcast.com
- 9. JAVA MEMORY LAYOUT(5/5) PERMGEN / META SPACE Class bytecodes Class metadata Runtime information Code Compilation Cache etc. www.hazelcast.com
- 10. G1 (GARBAGE FIRSTCOLLECTOR) GenerationalGC Heap splitted into same sized regions Everyregion is either Eden, Survivor or Tenured space www.hazelcast.com
- 11.
- 12. Off-Heap is a(continuously)self allocated, managed and freed directmemoryregion. Itis notunder controlof the JavaGarbageCollector and needs custom written allocation and cleanup of data-regions. Off-Heap can notbe used for allocation of Javaobjects. DEFINITION OF OFF-HEAP? www.hazelcast.com
- 13. I'M DUKE SKYWALKER I'MHERE TO RESCUE YOU! www.hazelcast.com
- 14. DIRECT MEMORY ACCESS? GIVE YOURSELFTO THE DARK SIDE www.hazelcast.com
- 15. DIRECT MEMORY ACCESS? AREYOU SERIOUS? Fastmemoryarea Notaffectingthe GC Officiallyavailable since Java1.4 Serialization overhead when storingobjects Limited by-XX:MaxDirectMemorySize www.hazelcast.com
- 16. WHY DO WENEED OFF-HEAP MEMORY? www.hazelcast.com
- 17. WHY DO WENEED OFF-HEAP MEMORY? Storingof huge datasets Zero-Copywrites to channels Lower pressure on GC /less GC pauses Storage Space onlylimited byRAM Compactdatarepresentation possible IPC SharedMemorywith Memory-Mapped-Files www.hazelcast.com
- 18.
- 19. OPTIONS FOR OFF-HEAPSTORAGE (1/3) JNI (Java Native Interface) int*buffer=(int*)malloc(1024* sizeof(int)); if(buffer==NULL)throwOutOfMemoryException(); for(inti=0;i<1024;i++) buffer[sizeof(int)*i]=i; free(buffer); www.hazelcast.com
- 20. OPTIONS FOR OFF-HEAPSTORAGE (2/3) (Direct)ByteBuffer ByteBufferbuffer=ByteBuffer.allocateDirect(1024*4); for(inti=0;i<1024;i++) buffer.putInt(i); //bufferisautomaticallyfreedbyGC www.hazelcast.com
- 21. OPTIONS FOR OFF-HEAPSTORAGE (3/3) sun.misc.Unsafe Unsafeunsafe=trickToRetrieveUnsafe(); longaddress=unsafe.allocateMemory(1024*4); for(inti=0;i<1024;i++) unsafe.putInt(address+4*i,i); unsafe.freeMemory(address); www.hazelcast.com
- 22.
- 23. ADVANTAGES ON-HEAP No messingwithmalloc Automatic Garbage Collection No need for Serialization www.hazelcast.com
- 24. DISADVANTAGES ON-HEAP Slowdown onhigh allocation rate Bigoverhead on smallobjects (header) Heavilydependingon GC Combination www.hazelcast.com
- 25. ADVANTAGES OFF-HEAP No limitation*insize Compactdatalayout Zero-Copysocketread/write possible Frameworks available to manage memory www.hazelcast.com
- 26. DISADVANTAGES OFF-HEAP Allocation isup to you Deallocation is up to you Datalayoutis up to you Serialization maybe required JNI requires native library www.hazelcast.com
- 27.
- 28. AVAILABLE FRAMEWORKS (1/5) ApacheDirectMemory TerracottaBigMemory HazelcastElasticMemory MapDB.org etc. www.hazelcast.com
- 29. AVAILABLE FRAMEWORKS (2/5) ApacheDirectMemory CacheService<String,String>cacheService=newDirectMemory<...>() .setNumberOfBuffers(10).newCacheService(); cacheService.put("MyKey","SomeValue"); Stringvalue=cacheService.get("MyKey"); www.hazelcast.com
- 30. AVAILABLE FRAMEWORKS (3/5) TerracottaBigMemory <ehcachexml:noNamespaceSchemaLocation="..." name="MyCacheDefinition"> <cachename="MyOffheapCache"maxBytesLocalOffHeap="2G"/> </ehcache> CacheManagercacheManager=newCacheManager(); CachedataStore=cacheManager.get("MyOffheapCache"); Elementelement=newElement("MyKey","SomeValue"); dataStore.put(element); Stringvalue=(String)dataStore.get("MyKey").getObjectValue(); www.hazelcast.com
- 31. AVAILABLE FRAMEWORKS (4/5) HazelcastOffheap <hazelcastxml:noNamespaceSchemaLocation="..."> <mapname="MyMap"> <storage-type>OFFHEAP</storage-type> </map> </hazelcast> HazelcastInstancehz=Hazelcast.newInstance(); //ReturnsaIMapextendsConcurrentMap Map<String,String>map=hz.getMap("MyMap"); map.put("MyKey","SomeValue"); Stringvalue=map.get("MyKey"); www.hazelcast.com
- 32.
- 33. FURTHER INFORMATION AVAILABLE TheMust-Read for Off-Heap http://bit.ly/must-read-off-heap PacketObjectDescription from IBM http://bit.ly/packet-objects CompactDatastructures (Martin Thompson) http://bit.ly/compact-datastructures C++ Like Performance for Serialization http://bit.ly/serialization-performance Tricks with DirectMemoryAccess in Java http://bit.ly/direct-memory-tricks www.hazelcast.com
- 34. THE OFF-HEAP JEP PROPOSAL MAYTHE FORCE BE WITH YOU. THE FORCE IS STRONG WITH THIS ONE. www.hazelcast.com
- 35. OFF-HEAP JEP PROPOSAL ByteBufferlike interface Fully64-bitsizes and offsets Compare-And-Swap operations Volatile and ordered operations Optionalboundingchecks Supports Memorymapping SupportForeign Function Interface (FFI) JEP www.hazelcast.com
- 36. OFF-HEAP JEP PROPOSAL- CODE EXAMPLE DISCLAIMER: PROVISIONAL API importjavax.direct.*; BytesFactoryfactory=createBytesFactory(); Bytesbytes=factory.boundsChecking(false).deallocationChecks(false) .freeOnGC(false).create(ByteOrder.LITTLE_ENDIAN,1024*4); for(inti=0;i<1024;i++) bytes.putVolatileInt(i); bytes.release(); www.hazelcast.com
- 37. OFF-HEAP JEP PROPOSAL ProposalDiscussionGroup http://bit.ly/offheap-ml ProposalText http://bit.ly/proposal-text FFI JEP 191 http://bit.ly/ffi-jep www.hazelcast.com
- 38.