A Deep Dive into ScyllaDB's Architecture
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This talk will cover ScyllaDB Architecture from the cluster-level view and zoom in on data distribution and internal node architecture. In the process, we will learn the secret sauce used to get ScyllaDB's high availability and superior performance. We will also touch on the upcoming changes to ScyllaDB architecture, moving to strongly consistent metadata and tablets.
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A Deep Dive into ScyllaDB's Architecture
- 1. ScyllaDB Architecture - built for speed Tzach Livyatan, VP Product
- 2. Tzach Livyatan ■ VP Product ScyllaDB ■ Love Databases and NoSQL ■ <cool hobby> Your photo goes here, smile :)
- 3. ■ High Availability ■ Data Modeling ■ Implementation Presentation Agenda Vestibulum congue Distributed Node HW Control
- 5. NoSQL – By Data Model Key / Value Redis, Aerospike, RocksDB Document store MongoDB, Couchbase Wide column store Scylla, Apache Cassandra, HBase, DynamoDB Graph Neo4j, JanusGraph Complexity 5
- 6. NoSQL– By Availability vs Consistency 6 Pick Two Availability Partition Tolerance Consistency PACELC: Latency vs Consistency
- 7. Cluster - Node Ring 7 Node 5 Node 1 Node 2 Node 4 Node 3
- 8. Data Replication ■ Replication Factor: number of nodes where data (rows and partitions) are replicated ■ Done automatically ■ Set for keyspace CREATE KEYSPACE mykeyspace WITH replication = { 'class': 'NetworkTopologyStrategy', 'replication_factor' : 3} AND durable_writes = true; 8
- 9. Replication Factor (RF) = 3 9 Node 5 Node 1 Node 2 Node 4 Node 3
- 10. Multiple Data Centers 10 USA DC Asia DC EU DC 'us_1' : 3, 'eu' : 3, 'asia' : 3
- 11. Consistency Level ■ CL: # of nodes that must acknowledge read/write ■ I.E.: 1, QUORUM, LOCAL_QUORUM, ALL ■ Tunable Consistency: CL set per operation 11
- 13. Cluster Level Read 13 CL =1
- 16. Data Modeling
- 17. CQL Example Query: SELECT * from heartrate_v10 WHERE pet_chip_id = 80d39c78-9dc0-11eb-a8b3-0242ac130003 LIMIT 1; SELECT * from heartrate_v10 WHERE pet_chip_id = 80d39c78-9dc0-11eb-a8b3-0242ac130003 AND time >= '2021-05-01 01:00+0000' AND time < '2021-05-01 01:03+0000'; 17 https://gist.github.com/tzach/7486f1a0cc904c52f4514f20f14d2a97
- 18. Wide Partition Example CREATE TABLE heartrate_v10 ( pet_chip_id uuid, owner uuid, time timestamp, heart_rate int, PRIMARY KEY (pet_chip_id, time) ); pet_chip_id time heart_rate 80d39c78-9dc0-11eb-a8b3-0242ac130003 2021-05-01 01:00:00.000000+0000 120 80d39c78-9dc0-11eb-a8b3-0242ac130003 2021-05-01 01:01:00.000000+0000 121 80d39c78-9dc0-11eb-a8b3-0242ac130003 2021-05-01 01:02:00.000000+0000 120 Partition Key Clustering Key 18
- 19. Architecture pet_chip_id time heart_rate 80d39c78-9dc0-11eb-a8b3- 0242ac130003 2021-05-01 01:00:00.000000+0000 120 80d39c78-9dc0-11eb-a8b3- 0242ac130003 2021-05-01 01:01:00.000000+0000 121 80d39c78-9dc0-11eb-a8b3- 0242ac130003 2021-05-01 01:02:00.000000+0000 120 Partitioner Hash Function Partition Key Token Range
- 21. Advance Data Modeling Materialized Views (MV) Secondary Index (SI) Change Data Capture (CDC) Collections User Defined Types Time To Live (TTL) …
- 22. 1. INSERT INTO heartrate (pet_chip_id, Owner, Time, heart_rate) VALUES (..); 2. INSERT INTO heartrate Base replica View replica Coordinator 3. INSERT INTO heartrate_by_owner View is another table 22
- 23. View is another table 2. SELECT * FROM heartrate_by_owner WHERE owner = ‘642a..’; Base replica View replica Coordinator 1. SELECT * FROM heartrate_by_owner WHERE owner = ‘642a..’; 23
- 24. Global Sec Index - Different Partition key 2. SELECT name FROM pet_by_owner_index WHERE owner = '642a..'; 3. SELECT * FROM heartrate_10 WHERE pet_chip_id in (...) AND time in (...) Base replica View replica Coordinator 1. SELECT * FROM heartrate_v10 WHERE owner = ‘642a..’;
- 25. Write Path - Replica 25
- 26. 26 Read Path - Replica SSTables Cache Memory Disk 1 2 3 4 5 … Bloom Filter 2.5
- 27. Storage - Log-Structured Merge Tree SStable 1 Time
- 28. Storage - Log-Structured Merge Tree SStable 1 Time SStable 2
- 29. SStable 1 SStable 2 SStable 3 Time SStable 4 SStable 1+2+3 Storage - Log-Structured Merge Tree
- 30. Implementation
- 31. ScyllaDB Design Decisions C++ instead of Java 1 2 All Things Async 3 Shard per Core 4 Unified Cache 5 I/O Scheduler 6 Autonomous C++
- 32. ScyllaDB Design Decisions 1 2 All Things Async 3 Shard per Core 4 Unified Cache 5 I/O Scheduler 6 Autonomous C++
- 33. ScyllaDB Design Decisions Shards 1 2 All Things Async 3 Shard per Core 4 Unified Cache 5 I/O Scheduler 6 Autonomous C++
- 34. Small, Medium, Large Machines Why larger nodes? ■ Time between failures is shorter ■ Ease of maintenance ■ No noisy neighbours ■ No virtualization, container overhead ■ No other moving parts ■ Scale up before out!
- 35. Linear Scale Ingestion Constant Time while volume & throughput double 2X 2X 2X 2X 2X
- 36. Network Comparison Kernel Cassandra TCP/IP Scheduler queue queue queue queue queue threads NIC Queues Kernel Traditional Stack SeaStar’s Sharded Stack Memory Application TCP/I P Task Scheduler queue queue queue queue queue smp queue NIC Queue DPDK Kernel (isn’t involved) Userspace Application TCP/I P Task Scheduler queue queue queue queue queue smp queue NIC Queue DPDK Kernel (isn’t involved) Userspace Application TCP/I P Task Scheduler queue queue queue queue queue smp queue NIC Queue DPDK Kernel (isn’t involved) Userspace Core Database Task Scheduler queue queue queue queue queue smp queue NIC Queue Userspace
- 37. ScyllaDB Has Its Own Task Scheduler Traditional Stack Scylla’s Stack Promise Task Promise Task Promise Task Promise Task CPU Promise Task Promise Task Promise Task Promise Task CPU Promise Task Promise Task Promise Task Promise Task CPU Promise Task Promise Task Promise Task Promise Task CPU Promise Task Promise Task Promise Task Promise Task CPU Promise is a pointer to eventually computed value Task is a pointer to a lambda function Scheduler CPU Scheduler CPU Scheduler CPU Scheduler CPU Scheduler CPU Thread Stack Thread Stack Thread Stack Thread Stack Thread Stack Thread Stack Thread Stack Thread Stack Thread is a function pointer Stack is a byte array from 64k to megabytes
- 38. ScyllaDB Design Decisions Cassandra Scylla Key cache Row cache On-heap / Off-heap Linux page cache SSTables Unified cache SSTables Complex Tuning 1 2 All Things Async 3 Shard per Core 4 Unified Cache 5 I/O Scheduler 6 Autonomous C++
- 39. ScyllaDB Design Decisions Cassandra Key cache Row cache On-heap / Off-heap Linux page cache SSTables 1 2 All Things Async 3 Shard per Core 4 Unified Cache 5 I/O Scheduler 6 Autonomous C++ App thread Kernel SSD Page fault Suspend thread Initiate I/O Context switch I/O completes Interrupt Context switch Map page Resume thread
- 40. ScyllaDB Design Decisions Query Commitlog Compaction Userspace I/O Scheduler Disk Max useful disk concurrency Queue Queue Queue 1 2 All Things Async 3 Shard per Core 4 Unified Cache 5 I/O Scheduler 6 Autonomous C++
- 41. ScyllaDB Design Decisions Memtable Seastar Scheduler Compaction Query Repair Commitlog SSD Compaction Backlog Monitor Memory Monitor Adjust priority Adjust priority WAN CPU 1 2 All Things Async 3 Shard per Core 4 Unified Cache 5 I/O Scheduler 6 Autonomous C++
- 42. Different types of loads ■ OLTP ● Small work items ● Latency sensitive ● involves narrow portion of the data ■ OLAP ● Large work items ● Throughput oriented ● Performed on large amounts of data
- 43. Workload Prioritization Load #3 800 shares Load #2 400 shares Load #1 200 shares
- 44. Scylla Design Decisions 1 2 All Things Async 3 Shard per Core 4 Unified Cache 5 I/O Scheduler 6 Autonomous C++
- 45. More than 1M req/sec on i4i.8xlarge https://github.com/scylladb/1m-ops-demo by Attila Tóth
- 46. 46 ■ Built for High Availability ■ Design to meet modern hardware ■ Use a fully async, share nothing, shard per core architecture ■ Superior throughput and consistent low latency ■ Expose internal scheduler to the user as Workload Prioritization Summary
- 47. Scylla vs Competition ■ 1/7th the cost ■ 26x better in a real life scenario ■ 10x volume ■ 9.3x throughput ■ 1/4x latency ■ 4 Scylla nodes vs 40 Cassandra ■ 2.5X cheaper ■ 11x better latency ■ 1/5th cost in a benchmark ■ 20x better real-life scenario ■ No throttling ■ No locking CockroachDB Google’s Bigtable DynamoDB Cassandra logscaled
- 48. Stay in Touch Tzach Livyatan tzach@scylladb.com https://twitter.com/TzachL https://github.com/tzach https://www.linkedin.com/in/tzach/