What happens on a cache miss?

The application reads the database and populates the cache.

How does an updated product price become visible?

The Catalog module invalidates or refreshes the affected cache entry.

When is brief staleness unacceptable?

When the business rule requires current values, such as authoritative price or stock validation.

Standalone conceptPatternChapter II · Data · Building block 11 of 16

Cache-aside

With cache-aside, the application checks the cache and loads from the authoritative store on a miss.

By Michael Meierhoff · Meierhoff Systems

Cache hitEntry exists.
Cache missRead database and populate cache.
Write changeDefine expiry or invalidation.

Context

Why this is important

Use cache-aside for repeated reads with an explicit freshness rule.

Read strategy with application-managed population, expiry and invalidation.

Shop example · Mapping

Cache-aside: hit, miss and invalidation

The Catalog module caches product reads; stock and price changes need suitable refresh rules.

This is how you read the picture

Cache hit direct response
Cache miss load through
Write change Freshness

Cache-aside: hit, miss and invalidation
Aspect	Meaning	Validation
Read	Check cache first.	Load miss from source.
Write	Update source.	Refresh cache deliberately.

The matrix shows the read and update paths.

Benefits & limitations

Helps if:

Repeated reads can be served from a cache.
The application needs to control population and invalidation.

Boundaries

Cache and source can temporarily contain different values.
A cache outage or concurrent misses can add load and latency.

In practice

Define the key, source of truth, expiry and tolerable staleness for the query. Avoid deriving cache keys from unvalidated input.
Implement hit and miss paths separately and decide how entries are invalidated or refreshed after changes. Limit concurrent refreshes when many requests miss the same entry.
Test misses, stale values, cache failures and concurrent initial queries; measure load and hit rate against the database.

Read the detailed explanation

On a hit, the application uses the cached value. On a miss, it reads the authoritative store, writes the value to the cache with an expiry and returns it. Write paths update the source first; cache invalidation or repopulation needs a defined rule.

Cache-aside is a read strategy that keeps the cache outside the source of truth. Stale data, stampedes, cache failures and negative caching must fit business freshness needs.

Cache-aside is a caching strategy; data ownership determines the source of truth on a miss.

Data ownership determines which source remains authoritative on a miss.

Check your understanding

Test yourself in three stages

ReadingCheck in the picture
What happens on a cache miss?
View the solution with justification
The application reads the database and populates the cache.
ApplyingTransferred to a new situation
How does an updated product price become visible?
View the solution with justification
The Catalog module invalidates or refreshes the affected cache entry.
EvaluateWeighing an alternative
When is brief staleness unacceptable?
View the solution with justification
When the business rule requires current values, such as authoritative price or stock validation.

Explore further

These building blocks continue the thoughts of this page.

References

Continue on the learning path

Next in Data & state: Polyglot Persistence.

16 Building blocks

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