Optimizing Latency-Sensitive Queries for Presto at Facebook: A Collaboration Between Presto & Alluxio
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Alluxio Global Online Meetup May 7, 2020 For more Alluxio events: https://www.alluxio.io/events/ Speakers: Rohit Jain, Facebook Yutian "James" Sun, Facebook Bin Fan, Alluxio For many latency-sensitive SQL workloads, Presto is often bound by retrieving distant data. In this talk, Rohit Jain, James Sun from Facebook and Bin Fan from Alluxio will introduce their teams’ collaboration on adding a local on-SSD Alluxio cache inside Presto workers to improve unsatisfied Presto latency. This talk will focus on: - Insights of the Presto workloads at Facebook w.r.t. cache effectiveness - API and internals of the Alluxio local cache, from design trade-offs (e.g. caching granularity, concurrency level and etc) to performance optimizations. - Initial performance analysis and timeline to deliver this feature for general Presto users. - Discussion on our future work to optimize cache performance with deeper integration with Presto
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Optimizing Latency-Sensitive Queries for Presto at Facebook: A Collaboration Between Presto & Alluxio
- 1. Optimizing Latency-Sensitive Queries for Presto at Facebook A Collaboration Between Presto & Alluxio Rohit Jain (Facebook), James Sun (Facebook), Bin Fan (Alluxio) 05/07/2020 Q&A: www.alluxio.io/slack
- 2. • Overview • Architecture and Problems • Re-architecture and solution • Performance • Introduce Alluxio Local Cache • Timeline
- 3. SELECT * FROM A, B WHERE A.k = B.k Storage A Distributed SQL (Compute) Engine Result
- 4. Presto is Open Source
- 5. Presto @ Facebook Scale 40K Servers ~ 1 EB data scan per day > 80% new ETL
- 6. Interactive Use Cases @ Facebook * Rapto r MySQL . . .joins allowed across heterogenous data sources Hive • presto-hive (Presto) • General-purpose dashboarding and adhoc queries • presto-raptor (Raptor) • Low-latency dashboarding and A/B testing • Usually 10X faster than Presto • The two use cases have the similar fleet sizes
- 7. • Overview • Architecture and Problems • Re-architecture and solution • Performance • Introduce Alluxio Local Cache • Timeline
- 8. Difference between Presto and Raptor: How Presto Works Driver Driver Planner/ Optimizer Scheduler Worker Worker Driver Worker HDFS Hive Metastore read/writeBlock workload balanced openFiles getPartitions getFiles SQL result
- 9. Difference between Presto and Raptor: How Raptor Works Driver Driver Planner/ Optimizer Scheduler Worker Worker Driver Worker KV Store Raptor Metastore getFiles read/writeBlock hard affinity Local SSD Background Job backup compaction / cleaning write thru. SQL result
- 10. Pros and Cons between Presto and Raptor Presto Raptor Pros Large-scale storage (EB) Low latency (sub-second) Independent storage and compute scale Refined metastore (file-level) Cons High latency (sub-minute) Mid-scale storage (PB) Coarse metastore (partition-level) Coupled storage and compute
- 11. • Overview • Architecture and Problems • Re-architecture and solution • Performance • Introduce Alluxio Local Cache • Timeline
- 12. New Architecture to Unify Presto and Raptor Driver Driver Planner/ Optimizer Scheduler Worker Worker Driver Worker HDFS Hive Metastore getFiles openFile/footer cache read/writeBlock soft affinity local data cache Local SSD Caching Low-overhead coordinator KV store file location/stats
- 13. • Random Node Scheduler • Best efforts to assign the same split to the same worker Affinity scheduling
- 14. • A common optimization technique is to cache working dataset closer to the compute node. • With lesser trips to remote storage should help with latencies and IO. Data Caching
- 15. • Facebook internal caching libraries • Open source solutions • Build our own Various Options
- 16. • Naïve solution • Copying files from remote storage on local storage • Merging files in the local storage to keep file count low File Merge Caching
- 17. File Merge Caching contd..
- 18. • Java based OSS library • Segment Based data caching: Reading, writing and evicting in smaller units. • Asynchronous operations • Pluggable eviction policies • Semantic aware caching Learnings
- 19. • A Java based OSS library • Segment Based data caching • Pluggable eviction policies • Configuration of various aspects, sizes, resources usage, eviction policies, etc. • Provide detailed stats regarding cache usage. • Caching should not become a point of failure. • Asynchronous operations. • Files management at the disk level. • Flash throughput limiter to avoid endurance issues. Collaboration with Alluxio
- 20. • Two full days worth of queries from the production cluster was shadowed to the test cluster. • Query Count: 17320 • 600 nodes cluster • 460GB per node was configured for data caching. • LRU eviction policy. • 1MB as the block size, meaning data is read, stored, and evicted in the 1 MB size. Benchmark
- 21. • Overview • Architecture and Problems • Re-architecture and solution • Performance • Introduce Alluxio Local Cache • Timeline
- 22. Benchmark result
- 23. • IO Savings • Data Size read for master branch run: 582 T Bytes • Data Size read for caching branch run: 251 T Bytes • Savings in Scans: 57% Benchmark result cond..
- 24. • Cache hit rate Benchmark result cont..
- 25. • Overview • Architecture and Problems • Re-architecture and solution • Performance • Introduce Alluxio Local Cache • Timeline
- 26. Confidential Use Only – Do Not Share Alluxio Overview • Open source data orchestration • Commonly used for data analytics such as OLAP on Hadoop • Started as a research project “Tachyon” in UC Berkeley
- 27. Confidential Use Only – Do Not Share 750 1 3 70 210 1080 Fast Growing Open Source Community v1.0 Feb ‘16 v0.6 Mar ‘15 v0.2 Apr ‘13 v0.1 Dec ‘12 v2.1 Nov ‘19 v1.8 Jul ‘18 Over 1000 Github Contributors Latest release: 2.2.0 in March 2020
- 28. Consumer Travel & TransportationTelco & Media TechnologyFinancial Services Retail & Entertainment Data & Analytics Services Deployed in Hundreds of Companies
- 29. Alluxio Local Cache: Architecture Local cache storage Alluxio Caching File System On Cache Hit External Storage Presto Worker On Cache Miss HDFS API Calls Alluxio Cache Manager External File System Presto Server JVM
- 30. • Seek-heavy read pattern is (non-sequential) • Segment (1MB by default) based caching (compared file size) • Presto server is highly concurrent by design • Light-weight & fine-grained locking across segments • Queries are bursty • Optional async write to cache I/O Challenges & Implementation
- 31. • Pluggable cache replace policies: • LRU, LFU • Pluggable cache storage options: • local file system: each segment -> one file • Rocksdb Cache Configuration
- 32. • Alluxio Local Cache is an embedded library • Shipped with Alluxio client jar since v2.2.0 • No extra server daemon required • Can be easily used in other JVM applications • Alluxio System supports full functionalities • Data policies: free, pin, TTL etc • Metadata caching and synching • Familiar Filesystem CLIs • Transformation service Alluxio Local Cache vs. Alluxio System
- 33. • Overview • Architecture and Problems • Re-architecture and solution • Performance • Introduce Alluxio Local Cache • Timeline
- 34. • Enable Presto + Alluxio Local Cache: • edit etc/catalog/hive.properties • available in next Presto release • Future work • Semantics-aware metadata caching • Performance tuning: CPU vs mem Timeline & Future Work cache.enabled=true cache.type=ALLUXIO cache.base-directory=/tmp/alluxio-cache
- 35. Recording of this talk will be available soonQ & A