Low Overhead Concurrency Control for Partitioned Main Memory Databases. Evan P. C. Jones Daniel J. Abadi Samuel Madden"

Transcription

1 Low Overhead Concurrency Control for Partitioned Main Memory Databases Evan P. C. Jones Daniel J. Abadi Samuel Madden"

2 Banks" Payment Processing" Airline Reservations" E-Commerce" Web 2.0"

3 Problem:" Millions of transactions per second"

4 Problem:" Millions of transactions per second"

5 Problem:" Millions of transactions per second" =! $$$$!

6 Alternative: H-Store Project" Redesign specifically for OLTP" Prototype: ~0X throughput" Idea: Remove un-needed features" Source: Stonebraker et. al, The End of an Architectural Era, VLDB "

7 H-Store: High Throughput OLTP" Redesign DB specifically for OLTP" Prototype: ~0X throughput" Main memory database" Concurrency control consumes ~30-40% of CPU time"

8 *!)# *!"# Q=02 I02 *$%++.+7# 87',+# $!)# $!"# (!)# 0Q=W2 0C=I2,)--("-,)'.("-,/$'0("- I`=L2 concurrency control! 30-40% (!"#!)# &22+% 3/"/-+% 0I=2!"# CPU Cycle Breakdown for Shore on TPC-C New Order! Source: Harizopoulos, Abadi, Madden and Stonebraker," OLTP Under the Looking Glass, SIGMOD 2008"

9 *!)# *!"# Q=02 I02 *$%++.+7# 87',+# $!)# $!"# (!)# 0Q=W2 0C=I2,)--("-,)'.("-,/$'0("- I`=L2 concurrency control! 30-40% (!"#!)# &22+% 3/"/-+% 0I=2!"# CPU Cycle Breakdown for Shore on TPC-C New Order! Source: Harizopoulos, Abadi, Madden and Stonebraker," OLTP Under the Looking Glass, SIGMOD 2008"

10 Speculative Concurrency Control" Eliminate fine-grained access tracking (locks or read/write sets)" Eliminate undo logs (where possible)" Up to 2X faster than locking for appropriate workloads!

11 Why Support Concurrency?" Use idle resources:" " disk stalls" " user stalls" main memory" stored procedures" Physical resources:" " multiple CPUs" " multiple disks" partition per core" Long running txns:" donʼt do them"

12 H-Store: Single thread engine" Assumptions:! Database divided into partitions" Transactions access one partition (mostly)" Mapping procedures to partitions is given" Total data fits in memory of N machines" Partitions are replicated on 2 machines"

13 System Overview" Clients H-Store Client Library Client Library Client Library

14 Single Partition Transaction" Client

15 Single Partition Transaction" Client 2

16 Single Partition Transaction" Client execute 2

17 Single Partition Transaction" Client execute 2 3

18 Single Partition Transaction" Client 4 execute 2 3

19 Single Partition Transaction" Client 4 execute 2 3 execute

20 Single Partition Transaction" Clients H-Store Client Library Client Library Client Library

21 Single Partition Transaction" Clients H-Store Client Library Client Library Client Library 2

22 Single Partition Transaction" Clients H-Store Client Library Client Library Client Library 2 3

23 Single Partition Transaction" Clients H-Store Client Library Client Library Client Library 4 2 3

24 Single Partition Transaction" Clients H-Store Client Library Client Library Client Library 4 2 3

25 Single Partition Transaction" Clients H-Store Client Library Client Library Client Library 4 2 3

26 Single Partition Transaction" Clients H-Store Client Library Client Library Client Library 4 2 3

27 Single Partition Transaction" Clients H-Store Client Library Client Library Client Library 4 2 3

28 Single Partition Transaction" Clients H-Store Client Library Client Library Client Library 4 2 3

29 Single Partition Transaction" Clients H-Store Client Library Client Library Client Library 4 2 3

30 Single Partition Transaction" Clients H-Store Client Library Client Library Client Library 4 2 3

31 Not Perfectly Partionable?" Example: users and groups" Many applications are mostly partitionable" e.g. TPC-C: % multi-partition transactions"

32 Distributed Transactions" Need two-phase commit (consensus)" Simple solution:" block until the transaction finishes" Introduces network stall (bad)"

33 Blocking Multi-Partition" Clients H-Store Client Library Client Library Client Library

34 Blocking Multi-Partition" Clients H-Store Client Library Client Library Client Library 2 2

35 Blocking Multi-Partition" Clients H-Store Client Library Client Library Client Library 2 2

36 Blocking Multi-Partition" Client 2 P P

37 Blocking Multi-Partition" Client 2 P 3 P

38 Blocking Multi-Partition" Client 2 P execute 3 P

39 Blocking Multi-Partition" Client 2 P execute 3 4 P

40 Blocking Multi-Partition" Client 2 5 P execute 3 4 P

41 Blocking Multi-Partition" Client 2 5 P execute 3 4 P

42 Blocking Multi-Partition" Client P execute 3 4 P

43 Blocking Multi-Partition" Client P execute execute 3 4 P

44 Blocking Multi-Partition" Client P execute execute 3 4 P network stall

45 Blocking Multi-Partition" Clients H-Store Client Library Client Library Client Library

46 Blocking Multi-Partition" Clients H-Store Client Library Client Library Client Library

47 Blocking Multi-Partition" Clients H-Store Client Library Client Library Client Library

48 Blocking Multi-Partition" Clients H-Store Client Library Client Library Client Library

49 Blocking Multi-Partition" Clients H-Store Client Library Client Library Client Library

50 Two-Phase Locking" + Execute non-conflicting txns during stall" + No need to order in advance! Locking overhead" Deadlocks" Optimization: turn off locks and undo logging when no multi-partition transactions"

51 Speculative CC" While waiting for commit/abort, speculatively execute other transactions" + No locks; no read/write sets" Need global transaction order" Cascading aborts"

52 Speculative Multi-Partition" Client 2 5 P execute 3 4 P

53 Speculative Multi-Partition" Client 2 5 P execute execute 3 4 P

54 Speculative Multi-Partition" Client 2 5 P execute execute 3 4 P

55 Speculative Multi-Partition" Client 2 5 P execute execute 3 4 P

56 Speculative Multi-Partition" Client P execute execute 3 4 P

57 Speculative Multi-Partition" Client P execute execute 3 4 P

58 Speculation Limitation" Transactions with multiple rounds of work: need network stall" Example:". Read x on partition, y on partition 2" 2. Update x = f(x, y); y = f(x, y)"

59 Speculative Multi-Partition" Clients H-Store Client Library Client Library Client Library

60 Speculative Multi-Partition" Clients H-Store Client Library Client Library Client Library 2 2 3

61 Speculative Multi-Partition" Clients H-Store Client Library Client Library Client Library

62 Speculative Multi-Partition" Clients H-Store Client Library Client Library Client Library

63 Speculative Multi-Partition" Clients H-Store Client Library Client Library Client Library

64 Speculative Multi-Partition" Clients H-Store Client Library Client Library Client Library

65 Speculative Multi-Partition" Clients H-Store Client Library Client Library Client Library

66 Speculative Multi-Partition" Clients H-Store Client Library Client Library Client Library

67 Microbenchmark" Two partitions of a single table" (id INTEGER PRIMARY KEY, value INTEGER) Client Load Generator

68 Microbenchmark" Single partition transaction:" " read/write keys on one partition" Multi-partition transaction:" " access half keys from each partition" single partition work = multi-partition work" No deadlocks, no aborts, no conflicts"

69 Throughput (transactions/s)" 30000" 25000" 20000" Speculation" 5000" Locking" 0000" 5000" Blocking" Locking 40% Conflicts" 0" 0" 20" 40" 60" 80" 00" % Multi-Partition"

70 30000 Transactions/second Speculation Blocking Locking % 20% 40% 60% 80% 00% Multi-Partition Transactions

71 TPC-C Based" ~% multi-partition transactions" More complex locking" Many conflicts" Some deadlocks" Some aborts"

72 Throughput (transactions/s)" 30000" 25000" Speculation" 20000" Blocking" 5000" 0000" Locking" 5000" 0" 2" 4" 6" 8" 0" 2" 4" 6" 8" 20" Warehouses"

73 Transactions/second Speculation Blocking Locking Warehouses

74 Speculative CC"! better for mostly partitionable apps on main memory DBs! Up to 2X throughput" No locking overhead" No deadlocks"

75 Speculation 0% aborts Speculation % aborts Speculation 3% aborts Speculation 5% aborts Speculation 0% aborts Blocking 0% aborts Locking 0% aborts Transactions/second % 20% 40% 60% 80% 00% Multi-Partition Transactions

76 Locking 0% conflict Locking 20% conflict Locking 60% conflict Locking 00% conflict Speculation Blocking Transactions/second % 20% 40% 60% 80% 00% Multi-Partition Transactions

77 Speculation Blocking Locking Transactions/second % 20% 40% 60% 80% 00% Multi-Partition Transactions

78 Model Blocking Model Speculate Model Locking Measured Blocking Measured Speculate Measured Locking Transactions/second % 20% 40% 60% 80% 00% Multi-Partition Transactions

79 Speculation Blocking Locking Transactions/second % 20% 40% 60% 80% 00% Multi-Partition Transactions

80 Speculation Local Speculation Blocking Locking Optimistic Transactions/second % 20% 40% 60% 80% 00% Multi-Partition Transactions

81 Transactions/second Speculation Blocking Locking Optimistic Warehouses