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Voldemort on Solid State Drives
- 1. Voldemort on Solid State Drives Vinoth Chandar, Lei Gao, Cuong Tran Linkedin Corp, Mountain View, CA
- 2. What is Voldemort? • Distributed key-value storage system • Based on Amazon Dynamo • Open source • https://github.com/voldemort/voldemort • Widely used • Several TB of data @ Linkedin • Eharmony, Nokia, JIVE Software etc. • We are on SSD!
- 3. SSD Migration • Improve average latency • 20 ms to 2 ms • Cluster expansion & data restoration • Improved 10x • 95th & 99th latencies shot up • 30ms to 130ms and 240ms to 380ms • GC Issues !! Client operations BDB Cleaner Retention Job BDB Cache App1 App2 .. AppN Server JVM Heap Linux
- 4. Benchmarking for SSD • Java based systems • Need for End-End Correlation • Linux page stealing • Use AlwaysPreTouch • Run Workload causing Fragmentation • Promotion failure more likely • Defragmentation costly • Run Workload with High memory churn • cost of CMS Initial Mark • High CMS initiating fraction • Factor in higher IO Parallelism • Sequential IO benchmarks no longer use single thread
- 5. Takeaways • GC impact significant • Big heaps = Big pauses • Longer runs to account for SSD GC • SSD is log structured • Worst case 2 ms • Special attention to 95th & 99th • Fragmentation eats up gains
Notes de l'éditeur
- Voldemort eng at Lnkd . 10 sec
- 20 sec. Set theme for talk. Not about distributed systems aspects. Experiences with Single node performance issues during SSD migration.
- 1 min. multi tenant. TODO : say explicitly “focus on diagram at the bottom”
- 2 min “Tackling these GC issues, gave us some intuitions for benchmarking java based applications on SSD”. In end-end correlation, “First of all, given Big data on SSD is relatively new, we need tools to correlate patterns across the stack and make sense out of it. For example – young gen pauses due to linux page stealing. Line up page scan data and system time components in young gen pause from gc log”
- 1 min