Keep CALM and CRDT On

Abstract

Despite decades of research and practical experience, developers have few tools for programming reliable distributed applications without resorting to expensive coordination techniques. Conflict-free replicated datatypes (CRDTs) are a promising line of work that enable coordination-free replication and offer certain eventual consistency guarantees in a relatively simple object-oriented API. Yet CRDT guarantees extend only to data updates; observations of CRDT state are unconstrained and unsafe. We propose an agenda that embraces the simplicity of CRDTs, but provides richer, more uniform guarantees. We extend CRDTs with a query model that reasons about which queries are safe without coordination by applying monotonicity results from the CALM Theorem, and lay out a larger agenda for developing CRDT data stores that let developers safely and efficiently interact with replicated application state.

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“…Sh. Laddad et al (2022a) highlighted the challenges in developing reliable distributed applications and proposed the use of CRDT as a promising approach to achieve coordination in distributed systems. The authors emphasised the limitations of CRDT in providing secure observations of data state.…”

“…However, Sh. Laddad et al (2022a) used the CALM theorem, while the present study contains certain tasks and formulae, but no theorems.…”