Getting Started with Hazelcast - Second Edition

Therein lies the problem

By insulating the database from the read load, a problem is introduced in the form of a cache consistency issue. How does the local data cache deal with data changing underneath it within the primary database? The answer is rather disappointing—it can't! The manifestation of issues will largely depend on the data needs of the application and how frequently the data changes, but typically, caching systems will operate in one of the following two modes to combat the problem:

• Time-bound cache: This holds entries for a defined period (time-to-live, popularly abbreviated as TTL)
• Write-through cache: This holds entries until they are invalidated by subsequent updates

Time-bound caches almost always have consistency issues, but ...