Causal Consistency

Synonyms

Causal consistency (CC); Causal memory; Causal-plus consistency (Causal+ consistency, C+C)

Definition

Causal consistency is a “Data Consistency Model” (q.v.) initially introduced for message passing (distributed) systems and later for shared memory systems. It ensures that, writes are observed by every party in the system in potential-causality order.

Potential-causality order is a global partial order of operations that tracks whether some operation may be influenced (caused) by some other operation. Formally, operation u potentially causally precedes operation v or, equivalently, operation v potentially causally depends on operation u if any of the following conditions hold (For simplicity, we drop “potentially” and shorten to “causally precedes” and to “causally depends” respectively. Similarly, “potential-causality order” will be shortened to “causality order.”):

• 1. Thread of Execution: u and v are two operations in a single thread of execution, and operation uexecuted...