RAMBO II

1
RAMBO II
Reconfigurable Atomic Memory for Basic Objects

• Rapidly Reconfigurable Atomic Memory for Dynamic
  Networks

Seth Gilbert with Nancy A. Lynch Alex A.
Shvartsman
2
Distributed Shared Memory
Read
Write(7)
Write(0)
3
Atomic Consistency
Read
Write(7)
Write(0)
4
Quorums
Read
Write(7)
5
Prior Work on Quorums

• Gifford (79) and Thomas (79)
• Upfal and Wigderson (85)
• majority sets of readers and writers
• Vitanyi and Awerbuch (86)
• matrices of single-writer/single-reader
  registers
• Attiya, Bar-Noy and Dolev (90/95)
• majorities of processors to implement
  single-writer/multi-reader objects in message
  passing systems

Static
6
Dynamic Atomic Memory
7
Other Dynamic Approaches

• Using consensus to agree on each operation
  Lamport
• Bad performance, read/write depend on consensus
• Virtual synchrony Birman 85 group communication
  many
• Slow view formation, delays reads/writes
• One join or failure may trigger view formation
• Quorum-based reads/writes over GC De Prisco, et
  al. 99
• New view must satisfy intersection requirements
• Single reconfigurer approaches Lynch, Shvartsman
  97, Englert, Shvartsman 00
• Single point of failure

8
Rambo

• Goal Atomic Shared Memory
• Long-term survivability
• Decouple read/write ops and reconfiguration
• fast read/write ops, even if recon slow
• Maximize dynamics
• Anyone can reconfigure
• Reconfigure at any time
• Arbitrary new configuration

9
Rambo II

• messages lost?
• messages delayed?

• frequent reconfiguration?
• clocks out of synch?

Rambo stabilizes
Network stabilizes
10
Rambo Architecture
write-ack
read/write upgrade
write
Recon
read
read-ack
Net
11
Reads and Writes
Value
Tag
Write Phase 1 choose tag Phase 2 send
tag/value
Read Phase 1 find tag/value Phase 2 send
tag/value
32
100
5
101
24
102
72
103
12
Reads and Writes
?
c6


c3
c4
c5
?
?
Largest tag 100
New tag 101
write(x, 7)
13
Configuration Upgrade
c3
c4


?


c5
?
?
largest tag 101
upgrade(5)
14
Performance Analysis

• Assume
• Read/Write operations always terminate in 8d

• network stabilizes
• reconfiguration-spacing
• configuration-viability
• etc.

Network stabilizes
Rambo stabilizes
15
Implementation
Rambo Rambo II
Latency
Frequency of Reconfiguration
16
Conclusions

• New algorithm for dynamic, reconfigurable atomic
  memory
• Provably atomic (in all executions)
• Good performance, when network stabilizes

17
Future Work

• Using Rambo
• Sensor networks
• Peer-to-Peer networks
• Wireless networks
• When to initiate reconfiguration?
• online algorithm
• Algorithmic refinements
• Reducing communication.
• Early return of read values.
• Backup strategies for when configuration-viability
  fails.

18
The End