Safety of a Server-Based Version Vector Protocol Implementing Session Guarantees

Abstract

Session guarantees are used to manage replica consistency of a distributed system from the client perspective. This paper defines formally the guarantees, presents and proves safety of a protocol implementing session guarantees using server-based version vectors.

Bounding Recovery Time in Rollback-Recovery Protocol for Mobile Systems Preserving Session Guarantees

“…Data consistency in rVsSG is managed by VsSG consistency protocol [BSW05], which uses a concept of server-based version vectors, having the following form:…”

“…By contradiction, let us assume that server S j has performed new operation o obtained from client C i , before performing again operation w, received during a former synchronization with other servers and lost because of S j failure. Due to underlying VsSG protocol [BSW05], the following condition must be fulfilled (line 9) to perform operation o: V Sj ≥ W . More precisely, when o is a read operation required with RYW session guarantee, or a write operation requiring MW, above condition is equivalent to ∀l :…”

“…For that reason, session guarantees [TDP + 94], also called client-centric consistency models, have been proposed to define required properties of the system observed from client's point of view. Four session guarantees have been defined: Read Your Writes (RYW), Monotonic Writes (MW), Monotonic Reads (MR) and Writes Follow Reads (WFR) and protocols implementing them have been introduced [TDP + 94,BSW05,Sob05]. Unfortunately these protocols assume that clients and servers are reliable and they do not crash.…”

“…To solve such a problem, we propose rVsSG protocol, integrating logging and checkpointing techniques with coherence operations of VsSG consistency protocol [TDP + 94,BSW05,Sob05]. Consequently, the proposed protocol offers the ability to overcome servers' failures transparently to the client, and preserves session guarantees at the same time.…”

Checkpointing and rollback-recovery protocol for mobile systems with MW session guarantee

“…According to our knowledge, none of existing consistency protocols for mobile environment which preserve session guarantees [2,10], is fault-tolerant. The lack of consistency protocols optimized in terms of rollbackrecovery, makes the construction of effective solutions adjusted to real applications requirements more difficult.…”