Scaling Your Cache And Caching At Scale
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The document discusses caching architecture, including its benefits, challenges, and performance testing. It covers key concepts such as memory hierarchy, eviction policies, and data consistency, as well as configurations for caching solutions like Ehcache and Terracotta. The presentation emphasizes the importance of understanding use cases and conducting proper testing to optimize cache efficiency and scalability.
Scaling Your Cache And Caching At Scale
- 1. Scaling Your Cache & Caching at Scale Alex Miller @puredanger
- 2. Mission • Why does caching work? • What’s hard about caching? • How do we make choices as we design a caching architecture? • How do we test a cache for performance?
- 4. Lots of data
- 5. Memory Hierarchy Clock cycles to access Register 1 L1 cache 3 L2 cache 15 RAM 200 Disk 10000000 Remote disk 1000000000 1E+00 1E+01 1E+02 1E+03 1E+04 1E+05 1E+06 1E+07 1E+08 1E+09
- 6. Facts of Life Register Fast Small Expensive L1 Cache L2 Cache Main Memory Local Disk Remote Disk Slow Big Cheap
- 7. Caching to the rescue!
- 8. Temporal Locality Hits: 0% Cache: Stream:
- 9. Temporal Locality Hits: 0% Cache: Stream: Stream: Cache: Hits: 65%
- 10. Non-uniform distribution Web page hits, ordered by rank 3200 100% 2400 75% 1600 50% 800 25% 0 0% Page views, ordered by rank Pageviews per rank % of total hits per rank
- 11. Temporal locality + Non-uniform distribution
- 12. 17000 pageviews assume avg load = 250 ms cache 17 pages / 80% of views cached page load = 10 ms new avg load = 58 ms trade memory for latency reduction
- 13. The hidden benefit: reduces database load Memory Database sio ning i rov er p o f ov line
- 14. A brief aside... • What is Ehcache? • What is Terracotta?
- 15. Ehcache Example CacheManager manager = new CacheManager(); Ehcache cache = manager.getEhcache("employees"); cache.put(new Element(employee.getId(), employee)); Element element = cache.get(employee.getId()); <cache name="employees" maxElementsInMemory="1000" memoryStoreEvictionPolicy="LRU" eternal="false" timeToIdleSeconds="600" timeToLiveSeconds="3600" overflowToDisk="false"/>
- 16. Terracotta App Node App Node App Node App Node Terracotta Terracotta Server Server App Node App Node App Node App Node
- 17. But things are not always so simple...
- 18. Pain of Large Data Sets • How do I choose which elements stay in memory and which go to disk? • How do I choose which elements to evict when I have too many? • How do I balance cache size against other memory uses?
- 19. Eviction When cache memory is full, what do I do? • Delete - Evict elements • Overflow to disk - Move to slower, bigger storage • Delete local - But keep remote data
- 20. Eviction in Ehcache Evict with “Least Recently Used” policy: <cache name="employees" maxElementsInMemory="1000" memoryStoreEvictionPolicy="LRU" eternal="false" timeToIdleSeconds="600" timeToLiveSeconds="3600" overflowToDisk="false"/>
- 21. Spill to Disk in Ehcache Spill to disk: <diskStore path="java.io.tmpdir"/> <cache name="employees" maxElementsInMemory="1000" memoryStoreEvictionPolicy="LRU" eternal="false" timeToIdleSeconds="600" timeToLiveSeconds="3600" overflowToDisk="true" maxElementsOnDisk="1000000" diskExpiryThreadIntervalSeconds="120" diskSpoolBufferSizeMB="30" />
- 22. Terracotta Clustering Terracotta configuration: <terracottaConfig url="server1:9510,server2:9510"/> <cache name="employees" maxElementsInMemory="1000" memoryStoreEvictionPolicy="LRU" eternal="false" timeToIdleSeconds="600" timeToLiveSeconds="3600" overflowToDisk="false"> <terracotta/> </cache>
- 23. Pain of Stale Data • How tolerant am I of seeing values changed on the underlying data source? • How tolerant am I of seeing values changed by another node?
- 24. Expiration TTI=4 0 1 2 3 4 5 6 7 8 9 TTL=4
- 25. TTI and TTL in Ehcache <cache name="employees" maxElementsInMemory="1000" memoryStoreEvictionPolicy="LRU" eternal="false" timeToIdleSeconds="600" timeToLiveSeconds="3600" overflowToDisk="false"/>
- 26. Replication in Ehcache <cacheManagerPeerProviderFactory class="net.sf.ehcache.distribution. RMICacheManagerPeerProviderFactory" properties="hostName=fully_qualified_hostname_or_ip, peerDiscovery=automatic, multicastGroupAddress=230.0.0.1, multicastGroupPort=4446, timeToLive=32"/> <cache name="employees" ...> <cacheEventListenerFactory class="net.sf.ehcache.distribution.RMICacheReplicatorFactory” properties="replicateAsynchronously=true, replicatePuts=true, replicatePutsViaCopy=false, replicateUpdates=true, replicateUpdatesViaCopy=true, replicateRemovals=true asynchronousReplicationIntervalMillis=1000"/> </cache>
- 27. Terracotta Clustering Still use TTI and TTL to manage stale data between cache and data source Coherent by default but can relax with coherentReads=”false”
- 28. Pain of Loading • How do I pre-load the cache on startup? • How do I avoid re-loading the data on every node?
- 29. Persistent Disk Store <diskStore path="java.io.tmpdir"/> <cache name="employees" maxElementsInMemory="1000" memoryStoreEvictionPolicy="LRU" eternal="false" timeToIdleSeconds="600" timeToLiveSeconds="3600" overflowToDisk="true" maxElementsOnDisk="1000000" diskExpiryThreadIntervalSeconds="120" diskSpoolBufferSizeMB="30" diskPersistent="true" />
- 30. Bootstrap Cache Loader Bootstrap a new cache node from a peer: <bootstrapCacheLoaderFactory class="net.sf.ehcache.distribution. RMIBootstrapCacheLoaderFactory" properties="bootstrapAsynchronously=true, maximumChunkSizeBytes=5000000" propertySeparator=",” /> On startup, create background thread to pull the existing cache data from another peer.
- 31. Terracotta Persistence Nothing needed beyond setting up Terracotta clustering. Terracotta will automatically bootstrap: - the cache key set on startup - cache values on demand
- 32. Pain of Duplication • How do I get failover capability while avoiding excessive duplication of data?
- 33. Partitioning + Terracotta Virtual Memory • Each node (mostly) holds data it has seen • Use load balancer to get app-level partitioning • Use fine-grained locking to get concurrency • Use memory flush/fault to handle memory overflow and availability • Use causal ordering to guarantee coherency
- 35. Scalability Continuum causal ordering YES NO NO YES YES 2 or more 2 or more 2 or more JVMS JVMSmore 2 or 2 or more big JVMs 2 or more JVMs 2 or more 2 or more 2 or more JVMs 2 or more JVMs JVMs of lots # JVMs 1 JVM 2 or more JVMS JVMs 2 or more JVMS JVMs JVMs JVMs of lots JVMs Terracotta runtime Ehcache Ehcache RMI Ehcache disk store OSS Terracotta FX Terracotta FX Ehcache FX Ehcache FX Ehcache DX Ehcache EX and FX management management and control and control more scale 21
- 36. Caching at Scale
- 37. Know Your Use Case • Is your data partitioned (sessions) or not (reference data)? • Do you have a hot set or uniform access distribution? • Do you have a very large data set? • Do you have a high write rate (50%)? • How much data consistency do you need?
- 38. Types of caches Name Communication Advantage Broadcast multicast low latency invalidation Replicated multicast offloads db Datagrid point-to-point scalable Distributed 2-tier point-to- all of the above point
- 39. Common Data Patterns I/O pattern Locality Hot set Rate of change Catalog/ low low low customer Inventory high high high Conversations high high low Catalogs/customers Inventory Conversations • warm all the • fine-grained • sticky load data into locking balancer cache • write-behind to DB • disconnect • High TTL conversations from DB
- 40. Build a Test • As realistic as possible • Use real data (or good fake data) • Verify test does what you think • Ideal test run is 15-20 minutes
- 41. Cache Warming
- 42. Cache Warming • Explicitly record cache warming or loading as a testing phase • Possibly multiple warming phases
- 43. Lots o’ Knobs
- 44. Things to Change • Cache size • Read / write / other mix • Key distribution • Hot set • Key / value size and structure • # of nodes
- 45. Lots o’ Gauges
- 46. Things to Measure • Application throughput (TPS) • Application latency • OS: CPU, Memory, Disk, Network • JVM: Heap, Threads, GC
- 47. Benchmark and Tune • Create a baseline • Run and modify parameters • Test, observe, hypothesize, verify • Keep a run log
- 49. Pushing It • If CPUs are not all busy... • Can you push more load? • Waiting for I/O or resources • If CPUs are all busy... • Latency analysis
- 50. I/O Waiting • Database • Connection pooling • Database tuning • Lazy connections • Remote services
- 51. Locking and Concurrency Threads Locks Key Value 1 ge 2 t2 3 get 2 4 5 6 put 8 7 8 12 9 ut 10 p 11 12 13 14 15 16
- 52. Locking and Concurrency Threads Locks Key Value get 2 1 2 get 2 3 4 5 6 put 8 7 8 9 10 put 12 11 12 13 14 15 16
- 53. Objects and GC • Unnecessary object churn • Tune GC • Concurrent vs parallel collectors • Max heap • ...and so much more • Watch your GC pauses!!!
- 54. Cache Efficiency • Watch hit rates and latencies • Cache hit - should be fast • Unless concurrency issue • Cache miss • Miss local vs • Miss disk / cluster
- 55. Cache Sizing • Expiration and eviction tuning • TTI - manage moving hot set • TTL - manage max staleness • Max in memory - keep hot set resident • Max on disk / cluster - manage total disk / clustered cache
- 56. Cache Coherency • No replication (fastest) • RMI replication (loose coupling) • Terracotta replication (causal ordering) - way faster than strict ordering
- 57. Latency Analysis • Profilers • Custom timers • Tier timings • Tracer bullets
- 58. mumble-mumble* It’s time to add it to Terracotta. * lawyers won’t let me say more
- 59. Thanks! • Twitter - @puredanger • Blog - http://tech.puredanger.com • Terracotta - http://terracotta.org • Ehcache - http://ehcache.org