What is caching and why is it important in a backend application?

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Accepted Answer

Caching is the practice of temporarily storing frequently accessed data in a fast storage layer to avoid recalculating or retrieving it from a slower source.

In a backend application, the cache typically sits between the application and the database. Instead of making an expensive database query every time, we first check if the data is in the cache. If it is, that is a cache hit and we return the data directly. If not, that is a cache miss and we query the database, then store the result in the cache.

The importance of caching is multifaceted.

First, latency reduction. In-memory caches like Redis respond in less than a millisecond, compared to several milliseconds for a database. For high-traffic APIs, this difference is significant.

Second, reduced load on the database. Every avoided query frees up resources. This allows supporting more users without scaling the database infrastructure.

Third, improved scalability. The cache can be distributed across multiple servers, enabling handling of traffic spikes.

Fourth, cost reduction. Fewer database queries potentially means smaller database servers.

The ideal data for caching is data that is frequently read but rarely modified, such as configurations, product catalogs, or user profiles. Data that changes constantly or must be absolutely current is not a good candidate for caching.