My Old Friend Malloc
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Today higher heaps and bigger RAM amounts are typical for standard Java server applications. We often then get to the limit of performance, predictability or GC pause times and using Off-Heap technologies we can lower that pains.
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My Old Friend Malloc
- 2. WHO AM I Christoph Engelbert(@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? Whydo we 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 A FAST 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 FIRST COLLECTOR) GenerationalGC Heap splitted into same sized regions Everyregion is either Eden, Survivor or Tenured space www.hazelcast.com
- 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'M HERE TO RESCUE YOU! www.hazelcast.com
- 14. DIRECT MEMORY ACCESS? GIVE YOURSELF TO THE DARK SIDE www.hazelcast.com
- 15. DIRECT MEMORY ACCESS? ARE YOU SERIOUS? Fastmemoryarea Notaffectingthe GC Officiallyavailable since Java1.4 Serialization overhead when storingobjects Limited by-XX:MaxDirectMemorySize www.hazelcast.com
- 16. WHY DO WE NEED OFF-HEAP MEMORY? www.hazelcast.com
- 17. WHY DO WE NEED 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
- 19. 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
- 20. OPTIONS FOR OFF-HEAP STORAGE (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-HEAP STORAGE (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
- 23. ADVANTAGES ON-HEAP No messingwith malloc Automatic Garbage Collection No need for Serialization www.hazelcast.com
- 24. DISADVANTAGES ON-HEAP Slowdown on high allocation rate Bigoverhead on smallobjects (header) Heavilydependingon GC Combination www.hazelcast.com
- 25. ADVANTAGES OFF-HEAP No limitation*in size Compactdatalayout Zero-Copysocketread/write possible Frameworks available to manage memory www.hazelcast.com
- 26. DISADVANTAGES OFF-HEAP Allocation is up to you Deallocation is up to you Datalayoutis up to you Serialization maybe required JNI requires native library www.hazelcast.com
- 28. AVAILABLE FRAMEWORKS (1/5) Apache DirectMemory TerracottaBigMemory HazelcastElasticMemory MapDB.org etc. www.hazelcast.com
- 29. AVAILABLE FRAMEWORKS (2/5) Apache DirectMemory CacheService<String,String>cacheService=newDirectMemory<...>() .setNumberOfBuffers(10).newCacheService(); cacheService.put("MyKey","SomeValue"); Stringvalue=cacheService.get("MyKey"); www.hazelcast.com
- 30. AVAILABLE FRAMEWORKS (3/5) Terracotta BigMemory <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) Hazelcast Offheap <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
- 33. FURTHER INFORMATION AVAILABLE The Must-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 MAY THE FORCE BE WITH YOU. THE FORCE IS STRONG WITH THIS ONE. www.hazelcast.com
- 35. OFF-HEAP JEP PROPOSAL ByteBuffer like 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 ProposalDiscussion Group http://bit.ly/offheap-ml ProposalText http://bit.ly/proposal-text FFI JEP 191 http://bit.ly/ffi-jep www.hazelcast.com