What are the main difficulties encountered when using cache in a system?

The main challenges when using cache in a system include:

• Data freshness (Cache coherence): data in the cache can become outdated if the source changes and the cache is not updated.
• Cache lifetime management (TTL): it is necessary to properly configure the data storage time to avoid frequent misses or outdated data.
• Synchronization complexity: in multi-threaded or distributed systems, it is necessary to correctly synchronize access to the cache.
• "Cold" cache problem: during the first startup or after clearing the cache, the system may operate slower.
• Choosing a caching strategy: for example, write-through, write-back, write-around — each has its pros and cons.
• Memory and resources: cache consumes additional memory, and it needs to be used efficiently.

Example: if caching database query results, it is necessary to ensure that when data in the database is updated, the cache is also updated or invalidated, otherwise the application may work with outdated information.