Cache & Distributed Cache
This section refers to how to implement caching features in the Umbraco application in a consistent way that will work in both single server environments and load balanced (multi-server) environments. The caching described in this section relates to application caching in the context of a web application only.
Please read this if you are Caching
Although caching is a pretty standard concept it is very important to make sure that caching is done correctly and consistently. It is always best to ensure performance is at its best before applying any cache and also beware of over caching as this can cause degraded performance in your application because of cache turnover.
In normal environments caching seems to be a pretty standard concept. If you are a package developer or developer who is going to publish a codebase to a load balanced environment then you need to be aware of how to invalidate your cache properly, so that it works in load balanced environments. If it is not done correctly then your package and/or codebase will not work the way that you would expect in a load balanced scenario.
If you are caching business logic data that changes based on a user's action in the backoffice and you are not using an _ICacheRefresher_** then you will need to review your code and update it based on the below documentation.**
Retrieving and Adding items in the cache
You can update and insert items in the cache.
Refreshing/Invalidating cache
The standard way to invalidate cache in Umbraco is to implement an ICacheRefresher
.
The interface consists of the following methods:
Guid RefresherUniqueId { get; }
Which you'd return your own unique GUID identifier
string Name { get; }
The name of the cache refresher (informational purposes)
void RefreshAll();
This would invalidate or refresh all caches of the caching type that this
ICacheRefresher
is created for. For example, if you were cachingEmployee
objects, this method would invalidate allEmployee
caches.
void Refresh(int Id);
This would invalidate or refresh a single cache for an object with the provided
int
id.
void Refresh(Guid Id);
This would invalidate or refresh a single cache for an object with the provided GUID id.
void Remove(int Id);
This would invalidate a single cache for an object with the provided
int
id. In many cases Remove and Refresh perform the same operation but in some casesRefresh
doesn't remove/invalidate a cache entry, it might update it.Remove
is specifically used to remove/invalidate a cache entry.
Some of these methods may not be relevant to the needs of your own cache invalidation so not all of them may need to perform logic.
There are 2 other base types of ICacheRefresher
which are:
ICacheRefresher<T>
- this inherits fromICacheRefresher
and provides a set of strongly typed methods for cache invalidation. This is useful when executing the method to invoke the cache refresher, when you have the instance of the object already since this avoids the overhead of retrieving the object again.void Refresh(T instance);
- this would invalidate/refresh a single cache for the specified object.void Remove(T instance);
- this would invalidate a single cache for the specified object.
IJsonCacheRefresher
- this inherits fromICacheRefresher
but provides more flexibility if you need to invalidate cache based on more complex scenarios (e.g. the MemberGroupCacheRefresher).void Refresh(string jsonPayload)
- Invalidates/refreshes any cache based on the information provided in the JSON. The JSON value is any value that is used when executing the method to invoke the cache refresher.
There are several examples of ICacheRefresher
's in the core: https://github.com/umbraco/Umbraco-CMS/tree/v9/dev/src/Umbraco.Core/Cache
Executing an ICacheRefresher
To execute your ICacheRefresher
you call these methods on the DistributedCache
instance (the DistributedCache
object exists in the Umbraco.Cms.Core.Cache
namespace):
void Refresh<T>(Guid cacheRefresherId, Func<T, int> getNumericId, params T[] instances)
This executes an
ICacheRefresher<T>.Refresh(T instance)
of the specified cache refresher Id
void Refresh(Guid cacheRefresherId, int id)
This executes an
ICacheRefresher.Refresh(int id)
of the specified cache refresher Id
void Refresh(Guid cacheRefresherId, Guid id)
This executes an
ICacheRefresher.Refresh(Guid id)
of the specified cache refresher Id
void Remove(Guid refresherGuid, int id)
This executes an
ICacheRefresher.Remove(int id)
of the specified cache refresher Id
void Remove<T>(Guid refresherGuid, Func<T, int> getNumericId, params T[] instances)
This executes an
ICacheRefresher<T>.Remove(T instance)
of the specified cache refresher Id
void RefreshAll(Guid refresherGuid)
This executes an
ICacheRefresher.RefreshAll()
of the specified cache refresher Id
So when do you use these methods to invalidate your cache?
This really comes down to what you are caching and when it needs to be invalidated.
What happens when an ICacheRefresher is executed?
When an ICacheRefresher
is executed via the DistributedCache
a notification is sent out to all servers that are hosting your web application to execute the specified cache refresher. When not load balancing, this means that the single server hosting your web application executes the ICacheRefresher
directly. However when load balancing, this means that Umbraco will ensure that each server hosting your web application executes the ICacheRefresher
so that each server's cache stays in sync.
Events handling to refresh cache
To use the extensions add a using to Umbraco.Extensions
; You can then invoke them on the injected DistributedCache
object.
IServerMessenger
The server messenger broadcasts 'distributed cache notifications' to each server in the load balanced environment. The server messenger ensures that the notification is processed on the local environment.
Getting and clearing cached content
See our example on how to cache tags.
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