Wyatt Lloyd will present his preFPO on Tuesday December 11 at 9AM in Room 402. The members of his committee are; Michael Freedman, advisor; Vivek Pai and David Andersen (CMU), readers; Jennifer Rexford and Margaret Martonosi, nonreaders. Everyone is invited to attend his talk. His abstract follows below. ------------------------------ Title: Stronger Consistency and Semantics for Low-Latency Geo-Replicated Storage Abstract: Distributed data stores that support complex online applications, such as social networks, are built with a two-level architecture. Data is replicated across a small number of datacenters and within each datacenter is stored in clusters of thousands or more machines. These two levels bring different challenges for creating a scalable, responsive, and consistent data store. Our COPS system is the first distributed data store to guarantee the ALPS properties—availability, low latency, partition tolerance, and scalability—and achieve consistency stronger than eventual. Eventual consistency specifies only that writes in one datacenter eventually show up in the others. Causal consistency, which is what COPS provides, maintains the partial order over operations establish by potential causality. Under causal consistency, all of a user’s operations appear in the order they are issued and interactions between users, e.g., conversations in comments, appear in their correct order as well. This improvement in consistency gives users a better experience and makes the data store easier for programmers to reason about. The key technical contribution of the COPS work is its fully distributed and scalable architecture that uses explicit metadata and off-path dependency checks to enforce ordering instead of relying on any single point of coordination. Our Eiger system pushes on the semantics an ALPS data store can provide. Eiger provides high-performance, guaranteed low-latency read-only and write-only transactions across all the machines in a cluster. Read-only transactions allow a client to observe a consistent snapshot of an entire cluster. Write-only transactions allow clients to atomically write many values spread across many servers at a single point in time. One important use case for write-only transaction is maintaing symmetrical relationships, e.g., Alice “isAFriendOf” Bob and Bob “isAFriendOf” Alice should both appear or disappear at the same time. Eiger also improves the semantics of ALPS data stores by providing the Column-Family data model—which is used in BigTable and Cassandra, and can be used to built real applications like Facebook—instead of the key-value data model provided by COPS—which is useful mainly as an opaque cache.