Write-Through Cache

What it is

Write-through caching updates the cache and the database as part of the write path. The cache mirrors the source of truth for the data it stores.

Why it matters

It avoids many stale-read problems from cache-aside because recently written data is immediately present in the cache. This gives readers a simpler mental model.

How it works

On write, the application or cache layer writes the new value to the cache and persists it to the database before acknowledging success.

When to use it

Use it for read-heavy data where writes are less frequent and freshness matters, such as account settings, entitlement records, or durable configuration.

Tradeoffs / failure modes

Writes are slower because two systems are involved. Partial failure handling is tricky: if the database write fails after the cache write, the cache can lie.

Tiny example

Updating a user’s notification preference writes the new value to Redis and the preferences table before returning success.

Related guides and systems

See Caching Strategies, Google Drive, GitHub, and Slack.