"Eventually consistent" is a term used in the context of distributed systems to describe a consistency model where updates to a data item are not immediately visible to all nodes in the system. Instead, there is a guarantee that, if no new updates are made to the data item, all accesses to that item will eventually return the last updated value. This model allows for high availability and performance at the cost of not always being able to read the most recent write operation immediately across all nodes.
In an eventually consistent system, when an update is made, it is first applied to one or more nodes. Due to the distributed nature of these systems, this update then needs to be propagated to other nodes. This propagation does not happen instantaneously; there is a delay during which different nodes may have different views of the data. However, the system guarantees that eventually, all nodes will converge to the same view, assuming no further updates are made during this period.
This model is particularly useful in scenarios where the system needs to remain highly available and responsive, even in the face of network partitions or delays. It is a trade-off that prioritizes availability and partition tolerance over immediate consistency, making it a suitable choice for many large-scale, distributed applications such as social media platforms, content delivery networks, and more.
Eventual consistency is part of the BASE (Basically Available, Soft State, Eventually Consistent) model, which is often used as an alternative to the traditional ACID (Atomicity, Consistency, Isolation, Durability) model in distributed systems. While ACID focuses on providing strong consistency guarantees, BASE allows for more flexibility by relaxing consistency requirements in favor of availability and performance[2][4].
