Exo-Leasing: Escrow Synchronization for Mobile Clients of Commodity Storage Servers

Abstract

Escrow reservations is a well-known synchronization technique, useful for inventory control, that avoids conflicts by taking into account the semantics of fragmentable object types. Unfortunately, current escrow techniques cannot be used on generic "commodity" servers because they require the servers to run the type-specific synchronization code. This is a severe limitation for systems that require applicationspecific synchronization but need to rely on generic components.Our exo-leasing method provides a new way to implement escrow synchronization without running any type-specific code in the servers. Instead, escrow synchronization code runs in the client providing the ability to use commodity servers. Running synchronization code in the client provides an additional benefit. Unlike any other system, our system allows a disconnected client to obtain escrow reservation from another disconnected client, reducing the need to coordinate with the servers. Measurements of a prototype indicate that our approach provides escrowbased conflict avoidance at moderate performance overhead.

Putting consistency back into eventual consistency

“…Indigo provides a set of basic techniques for achieving this, which extend previous ideas from the literature [17,32,35,39,44]. In comparison to the previous work, we not only combine these ideas in the same system, but we also propose a new implementation, which is optimized for a geo-replicated setting by requiring only peer-to-peer communication, and relying on CRDTs to manage information [38].…”

“…By enforcing local invariants in each transaction, they can guarantee that a global invariant is not broken. This idea can be applied to other data types, and it has been explored for supporting disconnected operation in mobile computing [35,39,44]. The demarcation protocol [6] is aimed at maintaining invariants in distributed databases.…”

“…Violation-avoidance extends escrow and reservation approaches [15,17,32,35,39]. The idea is that a replica coordinates in advance, to pre-allocate the permission to execute some collection of future updates, which (thanks to the reservation) will require no coordination.…”

Fabric

“…However, InterWeave has no support for information security. The work of Shrira et al [49] on exo-leases supports nested optimistic transactions in a client-server system with disconnected, multi-client transactions, but does not consider information security. MapJAX [37] provides an abstraction for sharing data structures between the client and server in web applications, but does not consider security.…”

Extending Eventually Consistent Cloud Databases for Enforcing Numeric Invariants

“…These parts are distributed among replicas, who can locally execute operations that do not exceed their allocated part. Unlike previous solutions that include some central authority and are often based on synchronous interactions between nodes [21], [5], [22], [25], our approach is completely decentralized and asynchronous, with each replica relying only on a local and possibly stale view of the information and on peer-to-peer asynchronous interactions. This design makes it easy to deploy our system, since we do not need to add a new master server (or replica group) that controls the allocation of operations on the counter.…”