Writes-Follow-Reads (Session Guarantee) WFR
Writes-follow-reads session guarantee of Terry et al. (PDIS 1994), sometimes called session causality: writes issued in a session are ordered after any writes whose effects were observed by earlier reads in that session (Viotti & Vukolić 2016, Eq. 25). One of the four session guarantees. Brzezinski et al. (2004) proved that causal consistency requires and includes all four session guarantees (so causal = PRAM ∧ writes-follow-reads), hence writes-follow-reads is strictly weaker than causal consistency.
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 weaker than
- Causal Consistency — Brzezinski et al. (2004) proved causal consistency requires and includes all four session guarantees, i.e. causal = PRAM ∧ writes-follow-reads (Viotti & Vukolić 2016, §3.4, Eq. 25). Causal consistency therefore implies writes-follow-reads while the converse fails, so writes-follow-reads is strictly weaker than causal consistency.
References
- Douglas B. Terry, Alan J. Demers, Karin Petersen, Mike Spreitzer, Marvin Theimer, Brent B. Welch. Session Guarantees for Weakly Consistent Replicated Data. Parallel and Distributed Information Systems (PDIS), 1994. doi:10.1109/PDIS.1994.331722
- Jerzy Brzezinski, Cezary Sobaniec, Dariusz Wawrzyniak. From Session Causality to Causal Consistency. Euromicro Workshop on Parallel, Distributed and Network-Based Processing (PDP), 2004. doi:10.1109/EMPDP.2004.1271440
- Paolo Viotti, Marko Vukolić. Consistency in Non-Transactional Distributed Storage Systems. ACM Computing Surveys 49(1), 2016. doi:10.1145/2926965