Garbage Collection and Eviction

Ferry enables you to selectively remove cached data that is no longer useful. The default garbage collection strategy of the Cache.gc() method is suitable for most applications, but the Cache.evict() method provides more fine-grained control for applications that require it.


The gc() method removes all objects from the normalized cache that are not reachable:

final cache = Cache();

To determine whether an object is reachable, the cache starts from all known root objects and uses a tracing strategy to recursively visit all available child references. Any normalized objects that are not visited during this process are removed. The gc() method returns a Set of the IDs of the removed objects.

Configuring garbage collection

You can use the retain() method to prevent an object (and its children) from being garbage collected, even if the object isn't reachable:


If you later want a retained object to be garbage collected, use the release() method:


If the object is unreachable, it will be garbage collected during next call to gc().


You can remove any normalized object from the cache using the evict() method:


You can also remove a single field from a cached object by providing the name of the field to remove:

cache.evict('my-object-id', fieldName: 'yearOfFounding');

Evicting an object often makes other cached objects unreachable. Because of this, you should call gc() after evicting one or more objects from the cache.