Cache hit

As explained in Latency

A cache hit occurs when requested data is found in the cache and can be returned without accessing the backing store.

A cache hit occurs when a lookup finds the requested value under its cache key. The application returns that value directly, avoiding the backing store and its slower lookup or computation. section 6.2

A cache hit is the fast path in cache-aside caching:

• The application looks up a cache key. section 6.3.1
• If the key exists and has not expired, the cache returns the value. section 6.3.1
• If the key is absent or expired, the application queries the backing store, transforms the result, and updates the cache. section 6.3.1
• Measure effectiveness with the cache hit-to-miss ratio; a low hit ratio can leave caching overhead without enough latency reduction. section 6.2

User lookup

An application uses a user ID as the cache key. On a hit, it returns the cached user information. On a miss, it reads the database, converts the result to JSON, and stores it under that user ID for later requests. section 6.3.1

Figure 6.1 With cache-aside caching, the client first looks up a key from the cache. On a cache miss, the client queries the database and updates the cache.

The request path makes the hit fast path and the miss path explicit: cache lookup first, followed by database retrieval and cache update only on a miss. section 6.3.1

How Latency covers it

How deep it goes

Defines hits, contrasts misses, explains hit-to-miss ratio, and traces cache-aside handling without detailing replacement-policy algorithms.

Examples

Uses user IDs, database records, JSON values, Redis, and REST API searches as concrete caching contexts.

What it assumes

Assumes cache keys, cached values, and a backing store; teaches the hit-versus-miss distinction directly.

What you can do after

Apply it via cache-aside caching by checking a key, reading a hit, or fetching and storing a miss.

How it connects

Connects cache hits to cache misses, cache-aside caching, backing stores, cache hit-to-miss ratio, and negative caching.

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Also explained in

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  Advanced Algorithms and Data StructuresA cache hit occurs when a requested data item is present in the cache and can be accessed there.
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  100 Go Mistakes and How to Avoid ThemA cache hit occurs when a requested memory location is found in the cache being checked.

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Related concepts

• cache misscontrasts with · A cache miss occurs when a lookup or access finds no usable requested item in the relevant cache, requiring retrieval or computation elsewhere.
• lazy initializationproduced by · Lazy initialization is a technique that postpones creating, retrieving, computing, or loading a value or resource until it is needed.
• cachinguses · Caching is the practice of storing reusable data or computation results so later access can avoid repeating retrieval or computation.
• conditional logicused by · Conditional logic is a programming technique that selects execution paths, actions, or result values according to evaluated conditions.

This explainer was generated by Manning's knowledge graph from the text of Latency. The section links point to the parts of the book it draws on.