PPT-CSE 486/586 Distributed Systems

Paxos 2 Steve Ko Computer Sciences and Engineering University at Buffalo Recap Paxos is a consensus algorithm It allows multiple acceptors accepting multiple proposals A proposer always makes sure that. Domain Name System. Steve Ko. Computer Sciences and Engineering. University at Buffalo. Last Time. Global states. A union of all process states. Consistent global state vs. inconsistent global state. Security --- 2. Steve Ko. Computer Sciences and Engineering. University at Buffalo. Recap. Three . types of functions. Cryptographic hash, symmetric key crypto, asymmetric key . crypto. Cryptographic hash. Concurrency Control --- 3. Steve Ko. Computer Sciences and Engineering. University at Buffalo. Recap. Strict execution of transactions?. Delay . both their read and write operations . on an . object until . Paxos. --- 2. Steve Ko. Computer Sciences and Engineering. University at Buffalo. Recap. Paxos. is a consensus algorithm.. It allows multiple acceptors accepting multiple proposals.. A proposer always makes sure that,. Paxos. --- 2. Steve Ko. Computer Sciences and Engineering. University at Buffalo. Recap. Paxos. is a consensus algorithm.. It allows multiple acceptors.. It allows multiple proposals to be accepted.. Consistency --- 2. Steve Ko. Computer Sciences and Engineering. University at Buffalo. Linearizability. vs. Sequential Consistency. Both care about giving . an illusion of a single copy. .. From the outside observer, the system should (almost) behave as if there’s only a single copy.. Case Study: Amazon Dynamo. Steve Ko. Computer Sciences and Engineering. University at Buffalo. Recap. CAP Theorem?. Consistency, Availability, Partition Tolerance. Pick two. Eventual consistency?. Availability and partition tolerance over consistency. New Trends in Distributed Storage. Steve Ko. Computer Sciences and Engineering. University at Buffalo. Recap. Two important components in a distributed file service?. Directory service. Flat file service. Case Study: . Facebook Haystack. Steve Ko. Computer Sciences and Engineering. University at Buffalo. Recap. DNS. Hierarchical servers. Root servers, top-level domain servers, authoritative servers. CDN. Gossiping. Steve Ko. Computer Sciences and Engineering. University at Buffalo. Recap. Consistency models. Linearizability. Sequential consistency. Causal consistency. Eventual consistency. Depending on application scenarios, one consistency model makes more sense that others.. Byzantine Fault . Tolerance --- 1. Steve Ko. Computer Sciences and Engineering. University at Buffalo. Recap. Digital certificates. Binds a public key to its owner. Establishes a chain of trust. TLS. Byzantine Fault Tolerance --- 1. Steve Ko. Computer Sciences and Engineering. University at Buffalo. Recap. Spanner. Geo-distributed database. Supports a relational data model with a SQL-like language. Paxos. --- 1. Steve Ko. Computer Sciences and Engineering. University at Buffalo. Recap. NFS. Caching with write-through policy at close(). Stateless server. One power efficient design: FAWN. Embedded CPUs & Flash . Mutual Exclusion --- 2. & Leader Election --- 1. Steve Ko. Computer Sciences and Engineering. University at Buffalo. 4. . Maekawa’s. Algorithm. Observation: . no need to have all peers reply. Only need to have .