What is the difference between cache consistency and cache coherence?

What is the difference between cache consistency and cache coherence?

Cache consistency refers to the uniformity of data across multiple caches, ensuring that all caches reflect the same data. Cache coherence, on the other hand, is about maintaining a consistent view of data in a shared memory system, ensuring that changes in one cache are visible to others.

Can you give an example of each?

Sure! An example of cache consistency is when multiple processors read from a shared variable, and any update to that variable is immediately visible to all processors. Cache coherence can be illustrated with a scenario where one processor updates a value in its cache, and other processors must ensure they either update their caches or invalidate the stale data.

Why is this important in distributed systems?

It's crucial because it affects the performance and reliability of data access in distributed systems. Without proper cache consistency and coherence, different parts of the system may operate on outdated or conflicting data, leading to errors and inefficiencies.

What are some common protocols used to maintain cache coherence?

Common protocols include MESI (Modified, Exclusive, Shared, Invalid), MOESI (Modified, Owner, Exclusive, Shared, Invalid), and MSI (Modified, Shared, Invalid). These protocols help manage how caches interact and maintain coherence.