1. Kite: Efficient and Available Release Consistency
for the Datacenter
Vasilis Gavrielatos, Antonios Katsarakis, Vijay Nagarajan, Boris Grot, Arpit Joshi*
University of Edinburgh, *Intel
Thanks to:

2. Key-Value Stores
Replicated KVS
Characteristics
● Read-Write-RMW API
● Highly Available
2

3. Key-Value Stores
Replicated KVS
Availability ≅ Nonblocking
Characteristics
● Read-Write-RMW API
● Highly Available
3

4. Key-Value Stores
Replicated KVS
Characteristics
● Read-Write-RMW API
● Highly Available
○ Replicated for fault tolerance
4

5. Key-Value Stores
Replicated KVS
Replication ⇒ Performance vs Consistency
Characteristics
● Read-Write-RMW API
● Highly Available
○ Replicated for fault tolerance
5

6. Performance Programmability
Weak
Consistency
Strong
Consistency
Consistency vs Performance
6

7. Performance Programmability
Weak
Consistency
Strong
Consistency
???
Consistency vs Performance
7

8. Existing Solution: Multiple Consistency Levels (MCL)
MCL Replicated KVS
Weak
Write
Strong
ReadAmazon DB
App Engine
PNUTS
Manhattan
Pileus
8

9. Amazon DB
App Engine
PNUTS
Manhattan
Pileus
Existing Solution: Multiple Consistency Levels (MCL)
MCL Replicated KVS
What about programming patterns?
Weak
Write
Strong
Read
9

10. The problem
MCL Replicated KVS
Alice
10

11. The problem
MCL Replicated KVS
Alice
void CreatePlayer( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
/// Player created
Write(player_created = true);
}
11

12. The problem
MCL Replicated KVS
Alice
If you can read the flag, then you
must be able to see the player!
void CreatePlayer( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
/// Player created
Write(player_created = true);
}
“the flag”
12

13. The problem
MCL Replicated KVS
void CreatePlayer( ) {
Write(name = “Leo”);
Write(surname = “Messi”);
Write(age = 32);
/// Player created
Write(player_created = true);
}
Alice
Fine by me!
13

14. The problem
MCL Replicated KVS
void CreatePlayer( ) {
Write(name = “Leo”);
Write(surname = “Messi”);
/// Player created
Write(player_created = true);
Write(age = 32);
}
Alice
No way!
14

15. The problem
MCL Replicated KVS
void CreatePlayer( ) {
Write(name = “Leo”);
Write(surname = “Messi”);
/// Player created
Write(player_created = true);
Write(age = 32);
}
Alice
There is no way to capture this with MCLs!
No way!
15

16. MCL Replicated KVS
Alice
MCL solution
void CreatePlayer( ) {
Strong_Write(age = 32);
Strong_Write(name = “Leo”);
Strong_Write(surname = “Messi”);
/// Player created
Strong_Write(player_created = true);
}
16

17. MCL Replicated KVS
Alice
Seems like an overkill...
MCL solution
void CreatePlayer( ) {
Strong_Write(age = 32);
Strong_Write(name = “Leo”);
Strong_Write(surname = “Messi”);
/// Player created
Strong_Write(player_created = true);
}
Missed performance opportunity
17

18. Shared Memory World
Sweet-spot in the Performance-vs-Consistency?
18

19. Sweet-spot in the Performance-vs-Consistency?
Shared Memory World
DRF-SC!
19

20. Programming paradigm: DRF-SC
Alice
Multiprocessor
20

21. DRF-SC
Programming
Paradigm
Alice
Programming paradigm: DRF-SC
Multiprocessor
21

22. DRF-SC
Programming
Paradigm
Alice
Programming paradigm: DRF-SC
Multiprocessor
Annotated synchronization ⇒ SC
22

23. Under the hood: Release Consistency
Alice
Releaseaa
Consistency
DRF-compliant
memory model
DRF-SC
Programming
Paradigm
Multiprocessor
23

24. Under the hood: Release Consistency
Alice
void CreatePlayer( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
/// Player created
Release(player_created = true);
}
Multiprocessor
24

25. Under the hood: Release Consistency
Alice
Multiprocessor
void CreatePlayer( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
/// Player created
Release(player_created = true);
}
Invariant: Writes appear to complete before the Release
25

26. Under the hood: Release Consistency
Alice
void ReadPlayer( ) {
Acquire(player_created);
Read(age);
Read(name);
Read(surname);
}
Bob
Multiprocessor
26

27. Under the hood: Release Consistency
Alice
Multiprocessor
void ReadPlayer( ) {
Acquire(player_created);
Read(age);
Read(name);
Read(surname);
}
Invariant: Reads appear to complete after the Acquire
Bob
27

28. RC Semantics
RC API Ordering
Read & Write none
Acquire acquire ⇒ all
Release all ⇒ release
28

29. Alice
Release
Consistency
DRF-compliant
memory model
DRF-SC
Programming
Paradigm
Can we do the same for KVSes?
Replicated KVS
29

30. Kite
Kite Replicated KVS
A Replicated KVS with
➢ Release Consistency
➢ High Availability
30

31. Our approach to building Kite
Steps
1 API mappings
2
31

32. Our approach to building Kite
Steps
1 API mappings
2 RC Semantics
32

33. Kite: API - Mappings
API Protocol
Reads
Writes
Acquire
Releases
Read-Modify-Writes
(RMWs)
33

34. Kite: API - Mappings
API Protocol
Reads
Writes
34

35. Kite: API - Mappings
API Protocol Overhead Consistency Availability
Reads Zero
Eventual
Consistency
High
Writes 1 Broadcast
35

36. Kite: API - Mappings
API Protocol Overhead Consistency Availability
Reads
Eventual Store
Zero
Eventual
Consistency
High
Writes 1 Broadcast
*
* Sebastian Burckhardt. 2014. Principles of Eventual Consistency 36

37. Kite: API - Mappings
API Protocol Overhead Consistency Availability
Reads
Eventual Store
Zero
Eventual
Consistency
High
Writes 1 Broadcast
Acquire Local
Linearizability High
Releases 1 Broadcast
37

38. Kite: API - Mappings
API Protocol Overhead Consistency Availability
Reads
Eventual Store
Zero
Eventual
Consistency
High
Writes 1 Broadcast
Acquire
ABD*
1 Broadcast*
Linearizability High
Releases 2 Broadcasts
*N. A. Lynch and A. A. Shvartsman. 1997. Robust emulation of shared memory using dynamic quorum-acknowledged broadcasts 38

39. Kite: API - Mappings
API Protocol Overhead Consistency Availability
Reads
Eventual Store
Zero
Eventual
Consistency
High
Writes 1 Broadcast
Acquire
ABD
1 Broadcast*
Linearizability High
Releases 2 Broadcasts
Read-Modify-Writes
(RMWs)
1 Broadcast Consensus High
39

40. Kite: API - Mappings
API Protocol Overhead Consistency Availability
Reads
Eventual Store
Zero
Eventual
Consistency
High
Writes 1 Broadcast
Acquire
ABD
1 Broadcast*
Linearizability High
Releases 2 Broadcasts
Read-Modify-Writes
(RMWs)
Paxos* 3 Broadcasts Consensus High
*Leslie Lamport. 1998. The part-time parliament. 40

41. Kite: API - Mappings
API Overhead Protocol
Reads Zero
Eventual Store
Writes 1 Broadcast
Acquire 1 Broadcast*
ABD
Releases 2 Broadcasts
Read-Modify-Writes
(RMWs)
3 Broadcasts Paxos
Common Case
Synchronization
Heavy
Synchronization
41

42. Our approach to building Kite
Steps
1 API mappings
2 RC Semantics
42

43. Kite: Fast-path/Slow-path
RC API Ordering
Read & Write none
Acquire acquire ⇒ all
Release all ⇒ release
RC Semantics

44. Kite: Fast-path/Slow-path
Fast-Path
Common operation
RC API Ordering
Read & Write none
Acquire acquire ⇒ all
Release all ⇒ release
RC Semantics

45. Kite: Fast-path/Slow-path
Fast-Path
Slow-Path When
slow
Common operation
RC API Ordering
Read & Write none
Acquire acquire ⇒ all
Release all ⇒ release
RC Semantics

46. Fast-path
Alice Bob
void CreatePlayer( )( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
Release(player_created = true);
}
46
void ReadPlayer( ) {
Acquire(player_created);
Read(age);
Read(name);
Read(surname);
}

47. Fast-path
Alice Bob
(age = 32, name = “Leo”, ….)
void CreatePlayer( )( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
Release(player_created = true);
}
47

48. Fast-path
Alice Bob
←(ack) ←(ack) ←(ack) ←(ack)
void CreatePlayer( )( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
Release(player_created = true);
}
48

49. Alice Bob
(Release (player_created = true))
void CreatePlayer( )( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
Release(player_created = true);
}
49
Fast-path

50. Alice Bob
(Release (player_created = true))
Before a release, gather all acks for prior writes
void CreatePlayer( )( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
Release(player_created = true);
}
50
Fast-path

51. Alice Bob
void ReadPlayer( ) {
Acquire(player_created);
Read(age);
Read(name);
Read(surname);
}
51
Fast-path

52. Alice Bob
(Acquire (player_created))
void ReadPlayer( ) {
Acquire(player_created);
Read(age);
Read(name);
Read(surname);
}
52
Fast-path

53. Alice Bob
(true)→ (true)→ (true )→ (true) →
void ReadPlayer( ) {
Acquire(player_created);
Read(age);
Read(name);
Read(surname);
}
53
Fast-path

54. Alice Bob
void ReadPlayer( ) {
Acquire(player_created);
Read(age);
Read(name);
Read(surname);
}
Local
Reads
54
Fast-path

55. Alice Bob
What if we cannot gather all acks before a release?
void ReadPlayer( ) {
Acquire(player_created);
Read(age);
Read(name);
Read(surname);
}
Local
Reads
55
Fast-path

56. Alice Bob
Fast-path ⇒ Slow-path
56

57. Alice Bob
void CreatePlayer( )( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
Release(player_created = true);
}
57
Fast-path ⇒ Slow-path

58. Alice Bob
(age = 32, name = “Leo”, ….)
void CreatePlayer( )( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
Release(player_created = true);
}
58
Fast-path ⇒ Slow-path

59. Alice Bob
←(ack) ←(ack) ←(ack)
void CreatePlayer( )( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
Release(player_created = true);
}
59
Fast-path ⇒ Slow-path

60. Alice Bob
void CreatePlayer( )( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
Release(player_created = true);
}
60
Fast-path ⇒ Slow-path

61. Alice Bob
(Node-5 is delinquent!)
void CreatePlayer( )( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
Release(player_created = true);
}
61
Fast-path ⇒ Slow-path

62. Alice Bob
←(ack) ←(ack) ←(ack)
5 = delinquent 5 = delinquent 5 = delinquent
void CreatePlayer( )( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
Release(player_created = true);
}
62
Fast-path ⇒ Slow-path

63. Alice Bob
(Release (player_created = true))
void CreatePlayer( )( ) {
Write(age = 32);
Write(name = “Leo”);
Write(surname = “Messi”);
Release(player_created = true);
}
5 = delinquent 5 = delinquent 5 = delinquent
63
Fast-path ⇒ Slow-path

64. Alice Bob
(Acquire (player_created))
5 = delinquent 5 = delinquent 5 = delinquent5 = delinquent 5 = delinquent 5 = delinquent
void ReadPlayer( ) {
Acquire(player_created);
Read(age);
Read(name);
Read(surname);
}
64
Fast-path ⇒ Slow-path

65. Alice Bob
(true, delinquent )→ (true, delinquent )→ (true, delinquent ) →
5 = delinquent 5 = delinquent 5 = delinquent5 = delinquent 5 = delinquent 5 = delinquent
void ReadPlayer( ) {
Acquire(player_created);
Read(age);
Read(name);
Read(surname);
}
65
Fast-path ⇒ Slow-path

66. Alice Bob
(Reset Delinquency)
Slow-path
I am delinquent!5 = delinquent 5 = delinquent 5 = delinquent5 = delinquent 5 = delinquent 5 = delinquent
void ReadPlayer( ) {
Acquire(player_created);
Read(age);
Read(name);
Read(surname);
}
66

67. Alice Bob
(Read age, name, ...)
void ReadPlayer( ) {
Acquire(player_created);
Read(age);
Read(name);
Read(surname);
}
I am delinquent!
67
Slow-path ⇒ Fast-path

68. Alice Bob
(32, “Leo”, ...)→ (32, “Leo”, ...)→ (32, “Leo”, ...)→
void ReadPlayer( ) {
Acquire(player_created);
Read(age);
Read(name);
Read(surname);
}
I am delinquent!
68
Slow-path ⇒ Fast-path

69. Alice Bob
I am not
delinquent
anymore!
void ReadPlayer( ) {
Acquire(player_created);
Read(age);
Read(name);
Read(surname);
}
69
Fast-path

70. Kite: Fast-path/Slow-path Recap
Fast path / Slow path mechanism
Before a Release
Gather all acks
➢ On timing-out, broadcast the delinquent machines
On an Acquire
Slow-path read / write
70

71. Fast path / Slow path mechanism
Before a Release
Gather all acks
➢ On timing-out, broadcast the delinquent machines
On an Acquire
Discover delinquency
➢ Slow-path if delinquent
Slow-path read / write
Kite: Fast-path/Slow-path Recap
71

72. Fast path / Slow path mechanism
Before a Release
Gather all acks
➢ On timing-out, broadcast the delinquent machines
On an Acquire
Discover delinquency
➢ Slow-path if delinquent
Slow-path read / write
➢ Add broadcast round
➢ Restore key to fast-path
Kite: Fast-path/Slow-path Recap
72

73. Kite’s Implementation
● RDMA-enabled
● Multi-threaded
● Asynchronous API
Infrastructure:
● Servers: 5 x (Intel Xeon E5-2630v4) with 64GB memory
● Network: 5 x 56 Gbit/s Infiniband NICs — 1 x 12-port Infiniband switch
Baseline:
● In-house ZAB implementation
○ RDMA-enabled, multi-threaded
Workloads:
1. Microbenchmarks
2. Lock-free data structures
Experimental Setup
73

74. Microbenchmarks
74

75. Microbenchmarks
75

76. Microbenchmarks
76

77. Kite
Microbenchmarks
77

78. 5% Sync
Microbenchmarks
78

79. 20% Sync & 5% RMW5% Sync
Microbenchmarks
79

80. 20% Sync & 5% RMW5% Sync
Microbenchmarks
80

81. Lock-free Data Structures
81
OperationspersecondnormalizedtoZAB

82. Kite: a replicated Key-Value Store with
● High availability &
● Release Consistency
Components:
● API mappings: Eventual Store, ABD & Paxos
● RC barrier semantics: Fast / Slow path
○ paper contains proof
Implementation features:
● Heavily multi-threaded
● RDMA-enabled
● Asynchronous API
● https://github.com/icsa-caps/Kite
Conclusion
Kite Replicated KVS
RDMA
82

83. Kite: a replicated Key-Value Store with
● High availability &
● Release Consistency
Components:
● API mappings: Eventual Store, ABD & Paxos
● RC barrier semantics: Fast / Slow path
○ paper contains proof
Implementation features:
● Heavily multi-threaded
● RDMA-enabled
● Asynchronous API
● https://github.com/icsa-caps/Kite
Conclusion
Kite Replicated KVS
RDMA
Thank you! Questions?
83

84. Back-up slides

85. 86

86. 87

87. Running Code on Kite
88

88. Write-only Throughput
89

89. Write-only Throughput with All-Aboard
90