Fail-safe Stale Reads¶

Fail-safe stale reads let your application keep serving the last local value when a refresh fails.

timeline
    title Local value lifetime
    Fresh window : return cached value
    Refresh attempt : try to load new value
    Fail-safe window : return stale value if refresh fails
    Expired : raise refresh error if refresh still fails

Each local entry has two deadlines:

After the fresh lifetime expires, Async Hybrid Cache tries to refresh the value. If the refresh raises an exception or times out and the stale value is still inside the fail-safe window, the stale value is returned.

If there is no stale value, or the fail-safe window has also expired, the refresh error is raised.