Relaxed Memory Model Zoo

Real-Time Causal Consistency (RTCausal)
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Real-Time Causal Consistency RTCausal

2011 · Mahajan, Alvisi, Dahlin · theoretical, formal · axiomatic formalism

A strengthening of causal consistency due to Mahajan, Alvisi & Dahlin: in addition to causality it enforces a real-time condition — causally concurrent writes that do not overlap in real time must be applied in their real-time order. Viotti & Vukolić (ACM Computing Surveys 2016, Eq. 28) express it as RealTimeCausality = Causality ∧ RealTime, so it is strictly stronger than causal consistency. It is incomparable to causal+: real-time causality does not imply strong convergence, and causal+ does not imply the real-time ordering (V-V §3.5, correcting Lloyd et al.'s original classification).

Properties

Property vector author-extrapolated — set only where the model’s definition pins the cell down (unknown cells are omitted); cells citing a specific source are marked.

Reasoning guarantees
  • no Coherence
Atomicity guarantees
  • no Multicopy atomic

Ordering relationships

Strictly stronger than
  • Causal Consistency — RealTimeCausality = Causality ∧ RealTime (Viotti & Vukolić 2016, Eq. 28; Mahajan, Alvisi & Dahlin 2011). It adds the requirement that causally concurrent, real-time-non-overlapping writes be applied in real-time order, disallowing strictly more behaviours, so causal consistency is strictly weaker than real-time causal consistency.
Incomparable with
  • Causal+ (Convergent Causal) Consistency — Causal+ and real-time causal consistency are incomparable (Viotti & Vukolić 2016, §3.5): real-time causality does not imply strong convergence, and causal+ does not impose real-time ordering — each forbids a behaviour the other allows. (V-V correct Lloyd et al.'s original claim that real-time causal is stronger than causal+.)

References

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