Semi-Linearizability Model Cuts Coordination Costs While Preserving Data Consistency

Semi-linearizability is a consistency model designed for geo-distributed systems that classifies operations into strong, weak, and semi categories based on their ordering requirements. Unlike traditional linearizability, which applies uniform global coordination to all operations, this approach reserves expensive consensus only for operations that genuinely require it. A prototype system called DeMon implements the model using causal broadcast for fast local operations, targeted consensus for critical ones, and vector-clock-style watermarks to reconcile the two paths. Benchmarks on the RUBiS workload show up to four orders of magnitude improvement in latency for common-case operations. The model is illustrated through an auction system where frequent Bid operations run locally and fast, while the rare CloseAuction operation uses consensus to ensure all relevant bids are correctly observed before a winner is determined.