Use Cases

HydraCache fits services where cache correctness depends on domain knowledge.

Expensive Async Work

Use get_or_load or cacheable_loader! when a value is expensive to compute and the application can name the value with a stable key.

Good examples:

• HTTP API responses keyed by tenant, endpoint, and parameters;
• generated reports keyed by tenant, date range, and permission scope;
• authorization or feature-flag lookups keyed by subject and context.

Database Query Results

Use hydracache-db or an adapter crate when a repository result is reusable and the application knows which writes make it stale.

Good examples:

• one user by id;
• one page of a tenant-scoped search;
• a small collection used on many requests;
• a repository method whose SQL or ORM shape should remain in application code.

Write-side Invalidation

Use tags when a write affects more than one cached key.

Examples:

• user:42 for one entity;
• users for collection-level reads;
• tenant:7 for tenant-wide invalidation;
• permission:abc for permission-scoped query families.

Request Storm Control

Use single-flight loaders when many requests can miss the same key at the same time. HydraCache lets one loader run while other callers join the in-flight work.

Local Near-cache Before Coordination

Use the local cache first. Add the invalidation bus or cluster APIs when several local caches need to react to the same invalidation intent.

Related terms: near cache, read-through cache, memoization, function caching, repository cache, query result cache, stale-if-error, stale while revalidate.