Reliable Multicast for Time-Critical Systems Mahesh Balakrishnan Ken Birman Cornell University.
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Transcript of Reliable Multicast for Time-Critical Systems Mahesh Balakrishnan Ken Birman Cornell University.
![Page 1: Reliable Multicast for Time-Critical Systems Mahesh Balakrishnan Ken Birman Cornell University.](https://reader035.fdocuments.in/reader035/viewer/2022062619/55176eca5503460e6e8b4e8c/html5/thumbnails/1.jpg)
Reliable Multicast for Time-Critical Systems
Mahesh BalakrishnanKen Birman
Cornell University
![Page 2: Reliable Multicast for Time-Critical Systems Mahesh Balakrishnan Ken Birman Cornell University.](https://reader035.fdocuments.in/reader035/viewer/2022062619/55176eca5503460e6e8b4e8c/html5/thumbnails/2.jpg)
Mission-Critical Datacenters
COTS DatacentersOnline e-tailers, search engines, corporate
applicationsWeb-services
Mission-Critical AppsNeed: Scalability, Availability, Fault-Tolerance
… Timeliness!
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The Time-Critical Datacenter
Migrating time-critical applications to commodity datacenters…
… conversely, providing datacenter web-services with time-critical performance.
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What’s a Time-Critical System?
Not ‘real time’, but ‘real fast’!
Financial calculators, military command and control… air traffic control (ATC)
… foobooks.com!
Technology Gap: Real-Time focuses on determinism, scale-up architectures
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The French ATC System
Mid to Late 90’s Teams of 3-5 air traffic controllers on a
cluster of desktop consoles 50-200 of these console clusters in an air
traffic control center Why study the French ATC?
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ATC Subsystems
Radar Image Weather Alert Track Updates Updates to Flight Plans Console to Console State Updates System Management and Monitoring ATC center to center Updates
Multicast ubiquitous…
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Two Kinds of Multicast
Virtually Synchronous Multicast: very reliable, not particularly fast
Unreliable Multicast: very fast, not particularly reliable
Nothing in between!
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Two Kinds of Subsystems
Category 1: Complete reliability (virtual synchrony) e.g: Routing decisions
Category 2: Careful application design + natural hardware properties + management policies. e.g: Radar
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Multicast in the French ATC
Engineering Lessons: Structure application to tolerate partial failures Exploit natural hardware properties
Can we generalize to modern systems?
Research Direction: Time-Critical Reliability Can we design communication primitives that
encapsulate these lessons?
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Anatomy of a Cloned Service
RACS
Updates multicast to whole group
Queries unicast to
single nodes
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Services An Amazon web-page is constructed by
100s of co-operating services*
Multicast is used for:Updating Cloned ServicesPublish-Subscribe / EventingDatacenter Management/Monitoring
* Werner Vogels, CTO of amazon.com, at SOSP 2005
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Multicast in the Datacenter
A node is in many multicast groups: One for each service it
hosts One for each topic it
subscribes to One or more
administration groups
Large Numbers of Overlapping Groups!
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Service Semantics
Product Popularity Service
Shipping Scheduler
Store Inventory
User History Service
Product Recommendations
User Profile Data
Data Store Services: stale data can result in overselling / underselling loss of real-world dollars
Cache Services: updated
periodically by back-end data-stores
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The Challenge
Datacenter Blades are failure-prone: Crash failures Byzantine behavior Bursty Packet Loss :
End-hosts kernels drop packets when subjected to traffic spikes.
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A New Reliability Model
Rapid delivery is more important than perfect reliability
Probabilistic Timeliness Graceful Degradation
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Wanted: a multicast primitive that
1. Scales to large numbers of arbitrarily overlapping multicast groups
2. Delivers multicasts quickly
3. Tolerates datacenter failure modes – bursty packet loss, node failures
4. Offers probabilistic properties
5. ‘Gives up’ on lost data after a threshold period
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Ricochet: Lateral Error Correction
Receivers exchange error correction XORs of multicast traffic
Works very well with multiple groups – scales upto a thousand groups per node
Probabilistic Timeliness: probability distribution of delivery
latencies
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Predictive Total Ordering (Plato)
Delivers messages to applications with no ordering delay in most cases
Orders messages only if there is a high probability of out-of-order delivery across different nodes
Probabilistic Timeliness: probability distribution of ordered delivery latency
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Performance
SRM takes seconds to recover lost packets
Ricochet recovers almost all packets within ~70 milliseconds
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Conclusion
Move from R/T to T/C yields huge benefits! Ricochet is faster… slashes latency… scalable… Clean delivery delay curve a powerful design tool,
replaced traditional hard (but conservative) limits We’re open for business:
Software and detailed paper available for download Give it a try… tell us what you think!
www.cs.cornell.edu/projects/quicksilver/ricochet.html