Creative Commons Attribution 4.0 International license
Sequential consistency (SC) is the prototypical correctness criterion for shared-memory systems. Deciding whether a finite execution history is SC is NP-complete [Gibbons and Korach, 1997]. In this brief announcement, we study the complexity of SC over infinite execution histories. It is known that SC is not among the safety properties [Glusman and Katz, 2001], which sit at the lowest level of the Borel hierarchy. We show that, under finite arrival, SC is in fact a liveness property. We further demonstrate that no deterministic transducer can compute sequential witnesses for all SC histories, nor can any infinite-state deterministic Büchi acceptor recognize SC. Finally, we establish that, under infinite arrival, SC for memories with unbounded registers and DCAS (double compare-and-swap) is 𝚺¹₁-complete.
@InProceedings{dimitrov:LIPIcs.DISC.2026.60,
author = {Dimitrov, Dimitar},
title = {{Brief Announcement: How Complex Can Sequential Consistency Be?}},
booktitle = {40th International Symposium on Distributed Computing (DISC 2026)},
pages = {60:1--60:6},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-454-3},
ISSN = {1868-8969},
year = {2026},
volume = {397},
editor = {Moses Jr., William K. and Censor-Hillel, Keren},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2026.60},
URN = {urn:nbn:de:0030-drops-281668},
doi = {10.4230/LIPIcs.DISC.2026.60},
annote = {Keywords: Distributed systems, Consistency, Complexity}
}