IMC Summit 2016 Breakout - Henning Andersen - Using Lock-free and Wait-free In-memory Algorithms to Turbo-charge High Volume Data Management
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The document describes how lock-free and wait-free in-memory algorithms can be used to improve performance of high-volume data management. It discusses using multi-version concurrency control (MVCC) with immutable data and wait-free index scans to enable concurrent transactions. A hash table with a skip list index is presented that allows lock-free inserts and finds using compare-and-swap operations while preserving consistency for readers. Transaction commit involves prepare, commit, finish and publish phases, with epochs and deferred reclamation used for garbage collection.
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IMC Summit 2016 Breakout - Henning Andersen - Using Lock-free and Wait-free In-memory Algorithms to Turbo-charge High Volume Data Management
- 1. USING LOCK-FREE AND WAIT-FREE IN-MEMORY ALGORITHMS TO TURBO-CHARGE HIGH VOLUME DATA MANAGEMENT HENNING ANDERSEN, STIBO SYSTEMS A/S See all the presentations from the In-Memory Computing Summit at http://imcsummit.org
- 2. BIO 20 years of professional career at Stibo Systems A/S Developed software for the last 30+ years Technical lead on many projects, including: Migrating from C++ to Java platform (performance & scalability) Establishing a component platform In-Memory component
- 3. GET TO KNOW STIBO SYSTEMS
- 5. 2015 MQ MDM OF PRODUCT DOMAIN
- 6. COMPLETE, SEAMLESS MULTIDOMAIN MDM SOLUTION
- 7. INTEGRATING IN-MEMORY INTO STEP STEP STEP STEP Server (J2EE) STEP Server (J2EE) DB Server STEP DB Server STEP In-Memory DB OFF-HEAP
- 8. BENCHMARK RESULTS Large Retailer Data Large Distributor Data Scalability Test Data
- 9. REQUIREMENTS Great performance Compact memory layout Data Per Entry Overhead Lookup by Key Complex Querying Indexing “Friendly” to our existing architecture Fast Startup/Initialization
- 10. PERFORMANCE BY SIMPLICITY MVCC/Immutability Wait-free index scans Code Generation Custom API/Direct Access mov (%rdi,%r11,1),%r11
- 11. BASIC HASH TABLE CLOSED ADDRESSING Next Key=K1 Value=10 hash(key)%tablesize Bucket Table
- 12. BASIC HASH TABLE CLOSED ADDRESSING Next Key=K1 Value=10 hash(key)%tablesize Next Key=K3 Value=20 Bucket Table
- 13. Next Key=K4 Value=30 BASIC HASH TABLE COLLISION hash(key)%tablesize Next Key=K3 Value=20Next Key=K1 Value=10 Bucket Table
- 14. MVCC HASH TABLE Next Prev TSN Key=K1 Value=10 hash(key)%tablesize TSN = Transaction Sequence Number Bucket Table Tx ID TSN Transaction Table Published TSN 2
- 19. Tx ID TSN MVCC HASH TABLE UPDATE - PUT(K1,15) Next Prev TSN=2 Key=K1 Value=10 hash(key)%tablesize Tx ID TSN UUID=1234 Bucket Table Transaction Table Prepare Finish Publish Next Prev Infinite Key=K1 Value=15 Prepare Published TSN 2
- 20. Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 MVCC HASH TABLE UPDATE - PUT(K1,15) Next Prev TSN=2 Key=K1 Value=10 hash(key)%tablesize Bucket Table Transaction Table Prepare Finish Publish Next Prev Infinite Key=K1 Value=15 Finish 1. Pull new TSN Published TSN 2
- 21. Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 MVCC HASH TABLE UPDATE - PUT(K1,15) Next Prev TSN=2 Key=K1 Value=10 hash(key)%tablesize Bucket Table Transaction Table Prepare Finish Publish Next Prev Infinite Key=K1 Value=15 Finish Next Prev TSN=3 Key=K1 Value=15 2. Apply TSN Published TSN 2
- 22. Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 MVCC HASH TABLE UPDATE - PUT(K1,15) Next Prev TSN=2 Key=K1 Value=10 hash(key)%tablesize Bucket Table Transaction Table Prepare Finish Publish Next Prev Infinite Key Value’ Finish Next Prev TSN=3 Key=K1 Value=15 3. Link to Prev Published TSN 2
- 23. Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 MVCC HASH TABLE UPDATE - PUT(K1,15) Next Prev TSN=2 Key=K1 Value=10 hash(key)%tablesize Bucket Table Transaction Table Prepare Finish Publish Next Prev Infinite Key Value’ Finish Next Prev TSN=3 Key=K1 Value=15 4. Update Bucket Table Published TSN 2
- 24. Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 MVCC HASH TABLE READER Next Prev TSN=2 Key=K1 Value=10 hash(key)%tablesize Bucket Table Transaction Table Prepare Finish Publish Next Prev Infinite Key Value’Next Prev TSN=3 Key=K1 Value=15 Reader TSN=2 Lookup K1 Published TSN 2
- 25. Prepare Finish Publish Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 MVCC HASH TABLE UPDATE (PUBLISH) Next Prev TSN=2 Key=K1 Value=10 hash(key)%tablesize Bucket Table Transaction Table Next Prev Infinite Key Value’Next Prev TSN=3 Key=K1 Value=15 Update Published TSN Publish Published TSN 23
- 26. Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 MVCC HASH TABLE READER Next Prev TSN=2 Key=K1 Value=10 hash(key)%tablesize Bucket Table Transaction Table Prepare Finish Publish Next Prev Infinite Key Value’Next Prev TSN=3 Key=K1 Value=15 Reader TSN=3 Lookup K1 Published TSN 3
- 27. MVCC HASH TABLE
- 28. INDEXING USING SKIP LISTS
- 29. SKIP LISTS H 10 20 30 40 50 50% have height >=225% have height >=3Head Height ~= log2(n) 30>=next.value? Find Value=30?
- 30. SKIP LISTS - INSERTION 20 30 40 50 15 Pick random height 10H
- 31. SKIP LISTS - INSERTION 20 30 40 50 15 Pick random height 10H
- 32. SKIP LISTS - INSERTION H 10 20 30 40 50 15 Pick random height
- 33. SKIP LISTS – INSERTION RESULT H 10 20 30 40 5015
- 34. Next Prev TSN=3 Key=K1 Value=15 Index Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 MVCC INDEXING USING SKIP LISTS hash(key)%tablesize Bucket Table Transaction Table Prepare Finish Publish Published TSN 22 Finish 5. Update Index Next Prev TSN=2 Key=K1 Value=10 Index
- 35. 5. Update Index Next Prev TSN=3 Key=K1 Value=15 Index Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 MVCC INDEXING USING SKIP LISTS hash(key)%tablesize Bucket Table Transaction Table Prepare Finish Publish Published TSN 22 Finish Next Prev TSN=2 Key=K1 Value=10 Index
- 36. SKIP LISTS – 5. UPDATE INDEX H 10 K1 P N 2 15 P N 3 20 K3 P N 2 30 K4 P N 2 40 K5 P N 2 50 K6 P N 2 Next Prev TSN Key Value Index L0 Index L1 Index L2 K1
- 37. SKIP LISTS – 5. UPDATE INDEX H 10 K1 P N 2 15 P N 3 20 K3 P N 2 30 K4 P N 2 40 K5 P N 2 50 K6 P N 2 Next Prev TSN Key Value Index L0 Index L1 Index L2 K1
- 38. SKIP LISTS – INSERTION RESULT H 10 K1 P N 2 15 P N 3 20 K3 P N 2 30 K4 P N 2 40 K5 P N 2 50 K6 P N 2 Next Prev TSN Key Value Index L0 Index L1 Index L2 K1
- 39. SKIP LISTS – FIND [12-25], TSN=2 H 10 K1 P N 2 15 P N 3 20 K3 P N 2 30 K4 P N 2 40 K5 P N 2 50 K6 P N 2 Next Prev TSN Key Value Index L0 Index L1 Index L2 K1
- 40. SKIP LISTS – FIND [12-25], TSN=3 H 10 K1 P N 2 15 P N 3 20 K3 P N 2 30 K4 P N 2 40 K5 P N 2 50 K6 P N 2 Next Prev TSN Key Value Index L0 Index L1 Index L2 K1
- 41. LOCK-FREE INSERTIONS SUMMARY CAS (compare-and-swap) on previous entity – one winner Bottom-up preserves skip-list for every level, allowing wait-free readers Help vacuum ensures lock-freedom H 10 20 30 40 15 17
- 42. LOCK-FREE INSERTIONS SUMMARY CAS (compare-and-swap) on previous entity – one winner Bottom-up preserves skip-list for every level, allowing wait-free readers Help vacuum ensures lock-freedom H 10 20 30 4015 17
- 43. Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 VACUUM, EPOCH BASED DEFERRED RECLAMATION hash(key)%tablesize Bucket Table Transaction Table Published TSN 23 H T 10 K1 P N 2 15 P N 3 20 K3 P N 2 30 K4 P N 2 40 K5 P N 2 50 K6 P N 2 K1 Snapshot Registry Reader TSN Epoch Thread=1234 2 17 Thread=1235 3 17Vacuum wait
- 44. Reader TSN Epoch Thread=1234 2 17 Thread=1235 3 17 Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 VACUUM, EPOCH BASED DEFERRED RECLAMATION hash(key)%tablesize Bucket Table Transaction Table Published TSN 23 H T 10 K1 P N 2 15 P N 3 20 K3 P N 2 30 K4 P N 2 40 K5 P N 2 50 K6 P N 2 K1 Snapshot Registry Vacuum wait
- 45. Reader TSN Epoch Thread=1235 3 17 Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 VACUUM, EPOCH BASED DEFERRED RECLAMATION hash(key)%tablesize Bucket Table Transaction Table Published TSN 23 H T 10 K1 P N 2 15 P N 3 20 K3 P N 2 30 K4 P N 2 40 K5 P N 2 50 K6 P N 2 K1 Snapshot Registry
- 46. Reader TSN Epoch Thread=1235 3 17 Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 VACUUM, EPOCH BASED DEFERRED RECLAMATION hash(key)%tablesize Bucket Table Transaction Table Published TSN 23 T 10 K1 P N 2 15 P N 3 20 K3 P N 2 30 K4 P N 2 40 K5 P N 2 50 K6 P N 2 K1 Snapshot Registry Vacuum phase 1 H
- 47. Reader TSN Epoch Thread=1235 3 17 Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 VACUUM, EPOCH BASED DEFERRED RECLAMATION hash(key)%tablesize Bucket Table Transaction Table Published TSN 23 T 10 K1 P N 2 15 P N 3 20 K3 P N 2 30 K4 P N 2 40 K5 P N 2 50 K6 P N 2 K1 Snapshot Registry Vacuum epoch wait H
- 48. Reader TSN Epoch Thread=2345 3 18 Thread=1235 3 17 Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 VACUUM, EPOCH BASED DEFERRED RECLAMATION hash(key)%tablesize Bucket Table Transaction Table Published TSN 23 T 10 K1 P N 2 15 P N 3 20 K3 P N 2 30 K4 P N 2 40 K5 P N 2 50 K6 P N 2 K1 Snapshot Registry Vacuum epoch wait H
- 49. Reader TSN Epoch Thread=2345 3 18 Thread=1235 3 17 Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 VACUUM, EPOCH BASED DEFERRED RECLAMATION hash(key)%tablesize Bucket Table Transaction Table Published TSN 23 T 10 K1 P N 2 15 P N 3 20 K3 P N 2 30 K4 P N 2 40 K5 P N 2 50 K6 P N 2 K1 Snapshot Registry Vacuum epoch wait H
- 50. Reader TSN Epoch Thread=2345 3 18 Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 VACUUM, EPOCH BASED DEFERRED RECLAMATION hash(key)%tablesize Bucket Table Transaction Table Published TSN 23 T 10 K1 P N 2 15 P N 3 20 K3 P N 2 30 K4 P N 2 40 K5 P N 2 50 K6 P N 2 K1 Snapshot Registry Vacuum epoch wait H
- 51. Reader TSN Epoch Thread=2345 3 18 Tx ID TSN UUID=1234 Tx ID TSN UUID=1234 3 VACUUM, EPOCH BASED DEFERRED RECLAMATION hash(key)%tablesize Bucket Table Transaction Table Published TSN 23 T 10 K1 P N 2 15 P N 3 20 K3 P N 2 30 K4 P N 2 40 K5 P N 2 50 K6 P N 2 K1 Snapshot Registry Vacuum phase 2 H
- 52. MVCC SUMMARY Map and indexes both under MVCC Index scans are wait-free (and simple/fast) Insert/update/delete are lock-free Automated reclamation of storage
- 53. EFFICIENT AND SAFE API transactionManager.read((snapshot) -> { QueryIterator<ProductCO> products = snapshot.query(ProductCO._ID.range(‘IMC’,’Stibo’)); while (products.next()) { CacheEntry<ProductCO> entry = queryIterator.entry(); long typeId = entry.longValue(ProductCO::getObjectType); CacheEntry<ObjectTypeCO> type = snapshot.get(typeId); // can do gets, queries etc. on the same snapshot safely for all kinds of objects } } public class ProductCO { long getObjectType(ValuePointer ptr) { … } } No object copies, no GC, efficient accessOften JVM can inline entire query to one native method 1 2 3 4 5
- 54. DIY USEFUL LEARNING • Memory model (java different from C++) and CAS operations • Assembly • CPU memory architecture • Wait-free and lock-free algorithms • Enumerate all states • Think about state transitions • Try to formally proof it right • Deletions are often the most tricky part • Do not even think about “this will never happen”, because it will
- 55. IN-MEMORY VENDOR QUESTIONS Direct access to data or only access to copies of data? And direct access to individual fields in an entry? Index/Query engine MVCC consistent with map gets and/or additional queries? Will index scans/queries acquire locks? Will index inserts acquire locks? Will map get/put operations acquire locks? Memory overhead per entry? Memory overhead per index (per entry)? How do you avoid memory fragmentation? Do you lock pages in memory and use huge/large pages?