Direct memory jugl-2012.03.08
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Apache Direct Memory is an open source implementation of off-heap caching that uses ByteBuffer.allocateDirect to store objects in off-heap memory without degrading JVM performance. It provides a multi-layered caching solution and can be used to build a standalone cache server similar to Memcached. Current use cases include integrating with Ehcache for multi-level caching and implementing an off-heap output stream to process streaming data without filling heap memory. Future work includes benchmarking, improving the API, and integrating with more libraries.
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Direct memory jugl-2012.03.08
- 1. JUG Lausanne 8. March 2012 Apache Direct Memory Reducing Heap Memory Stress The next battle horse for JVM performance tuning
- 2. JUG Lausanne 8. March 2012 About me • Benoit Perroud • Apache Direct Memory Commiter • [email protected] • @killerwhile • Software craftsman • BigData Engineer @
- 3. JUG Lausanne 8. March 2012 Today's Agenda • Off Heap Caching – Java Memory – Garbage Collector (GC) – Cache On-heap vs. Off-heap Caching • Apache Direct Memory – Design and principles – Uses cases • Multi layered cache • Standalone server “à la memcache” – Next steps • Questions
- 4. JUG Lausanne 8. March 2012 Before starting • Sorry for my bad English and my poor French • Interrupt me anytime • I have nothing to sell. It's just worth while sharing • Please do ask questions
- 5. JUG Lausanne 8. March 2012 Java Memory • Automatic memory allocation • Garbage collector (GC)
- 6. JUG Lausanne 8. March 2012 Garbage Collector • Several types of GC – Serial GC – Parallel GC (throughput collector) – Concurrent Mark & Sweep GC (concurrent low pause collector) – G1 GC (low latency concurrent M&S)
- 7. JUG Lausanne 8. March 2012 Garbage Collector • But all GC have a stop-the-world behavior • Proportional to the memory's size • Resulting in application unresponsiveness – A pain when dealing with tight SLAs
- 8. JUG Lausanne 8. March 2012 Cache On-Heap vs. Off-Heap • On-heap – Objects tends to be promoted into tenured memory – GC storm effect when using refreshing cache – No overhead (for caching by reference)
- 9. JUG Lausanne 8. March 2012 On-Heap vs. Off-Heap • Off-heap – Object payload is no more affecting GC – Serialization/Deserialization overhead • Hopefully lots of work on serialization has been done (Protobuf, Avro, Thrift, msgpack, BSON, ...)
- 10. JUG Lausanne 8. March 2012 Apache Direct Memory Apache Direct Memory is a multi layered cache implementation featuring off-heap memory storage to enable caching of java objects without degrading jvm performance. → Opensource implementation of Terracotta BigMemory.
- 11. JUG Lausanne 8. March 2012 Apache Direct Memory • Apache Software Foundation Incubator project • Met the Incubator falls 2011 • 12 developers ATM, 10+ contributors • I joined 1st January 2012 – was the good achievement of my Hacky Christmas Holiday :) • Disclaimer : Under heavy development – I rewrote most of the memory allocation service – APIs are subject to changes, and bugs to be found
- 12. JUG Lausanne 8. March 2012 Design & Principles • ByteBuffer.allocateDirect is the foundation of the cache • ByteBuffers are allocated in big chunk and then splitted for internal use
- 13. JUG Lausanne 8. March 2012 Design & Principles • Build on layers : – CachingService • Serialize object (pluggable) – MemoryManagerService • Compute access statistics – ByteBufferAllocatorService • Eventually deal with ByteBuffers
- 14. JUG Lausanne 8. March 2012 ByteBuffers Allocation 2 different allocation's strategies • Merging ByteBuffers allocation – No memory wasted – Free at creation – Suffer from fragmentation – Need synchronization at allocation and deallocation
- 15. JUG Lausanne 8. March 2012 ByteBuffers Allocation • Fixed size ByteBuffers allocation – Linux kernel SLAB's style allocation • Select a set of fixed sizes • Split bigger buffers (1MB+) in that size – Allocation is really fast and good concurrency • All structures is pre-instanciated – Creation (or buffer's size increase) has a cost • 1GB split in 128 bytes slabs is 8M+ buffers created – Do not suffer from fragmentation – Waste memory if the selected size is not relevant • Work really well in HDFS where all blocks are of the same size
- 16. JUG Lausanne 8. March 2012 Use case 1 : Multi layers cache • Idea : most used objects are cached on-heap, the rest off-heap, may overflown to disk. • Sounds like BigMemory. • See net.sf.ehcache.store.offheap.OffHeapStore • Actually we inject DM in ehcache like do BigMemory. Ouch ;) • Comparison needs to be done
- 17. JUG Lausanne 8. March 2012 Use case 2 : OffHeap Output Stream • Idea : read Twitter firehose stream without filling the precious heap memory – OOM will lead to unpredictable behavior else where in the application • From your socket directly write off-heap using OutputStream style – allocate a fixed size temporary buffer of your choice • Read from this stream – InputAndOutputStream parent class that holds both OutputStream and InputStream instances
- 18. JUG Lausanne 8. March 2012 Use case 3 : Standalone cache server • Idea : replace Memcached :) – But with native plain REST API • DM has all the building blocks to implement such server, worth while trying • See the server submodule
- 19. JUG Lausanne 8. March 2012 Next Steps • JSR 107 • Real Benchmarks • Builder patterns • Integration with more libs (Spring, Guice, …) • Implementations with DM lib (Cassandra (wip), Lucene, Tomcat, …) • Cache Resizing • Management and monitoring • ... • https://issues.apache.org/jira/browse/DIRECTMEMORY
- 20. JUG Lausanne 8. March 2012 Questions ? • Thanks for you attention