= Infinispan marshalling changes

Marshalling is the process of converting Java objects into bytes to send them across the network between {project_name} servers.
With {project_name} 26, the marshalling library has changed from JBoss Marshalling to Infinispan Protostream.
The libraries are not compatible between each other and, it requires some steps to ensure the session data is not lost.

WARNING: JBoss Marshalling and Infinispan Protostream are not compatible with each other and incorrect usage may lead to data loss.
Consequently, all caches are cleared when upgrading to this version.

To prevent losing user sessions upgrade to Keycloak 25 first and enable the persistent sessions feature as outlined in the migration guide for {project_name} 25.

= Operator no longer defaults to proxy=passthrough

The Operator will no longer default to the hostname v1 setting of proxy=passthrough. This allows deployments using hostname v2 for a fixed edge hostname to work as desired without additional options.

= New method in `ClusterProvider` API

The following method was added to `org.keycloak.cluster.ClusterProvider`:

* `void notify(String taskKey, Collection<? extends ClusterEvent> events, boolean ignoreSender, DCNotify dcNotify)`

When multiple events are sent to the same `taskKey`, this method batches events and just perform a single network call.
This is an optimization to reduce traffic and network related resources.

In {project_name} 26, the new method has a default implementation to keep backward compatibility with custom implementation.
The default implementation performs a single network call per an event, and it will be removed in a future version of {project_name}.

= Group-related events no longer fired when removing a realm

With the goal of improving the scalability of groups, they are now removed directly from the database when removing a realm.
As a consequence, group-related events like the `GroupRemovedEvent` are no longer fired when removing a realm.

If you have extensions handling any group-related event when a realm is removed, make sure to use the `RealmRemovedEvent` instead
to perform any cleanup or custom processing when a realm, and their groups, are removed.

The `GroupProvider` interface is also updated with a new `preRemove(RealmModel)` method to force implementations to properly
handle the removal of groups when a realm is removed.

= Operator scheduling defaults

Keycloak Pods will now have default affinities to prevent multiple instances from the same CR from being deployed on the same node, and all Pods from the same CR will prefer to be in the same zone to prevent stretch cache clusters.

= Operator's default CPU and memory limits/requests

In order to follow the best practices, the default CPU and memory limits/requests for the Operator were introduced. It affects both non-OLM and OLM installs. To override the default values for the OLM install, edit the `resources` section in the operator's https://github.com/operator-framework/operator-lifecycle-manager/blob/master/doc/design/subscription-config.md#resources[subscription].

= Deprecations in `keycloak-common` module

The following items have been deprecated for removal in upcoming {project_name} versions with no replacement:

- `org.keycloak.common.util.reflections.Reflections.newInstance(java.lang.Class<T>)`
- `org.keycloak.common.util.reflections.Reflections.newInstance(java.lang.Class<?>, java.lang.String)`
- `org.keycloak.common.util.reflections.SetAccessiblePrivilegedAction`
- `org.keycloak.common.util.reflections.UnSetAccessiblePrivilegedAction`

= Consistent usage of UTF-8 charset for URL encoding

`org.keycloak.common.util.Encode` now always uses the `UTF-8` charset for URL encoding instead relying implicitly on the `file.encoding` system property.

= Configuring the LDAP Connection Pool

In this release, the LDAP connection pool configuration relies solely on system properties. The main
reason is that the LDAP connection pool configuration is a JVM-level configuration rather than specific to an individual
realm or LDAP provider instance.

Compared to previous releases, any realm configuration related to the LDAP connection pool will be ignored.
If you are migrating from previous versions where any of the following settings are set to your LDAP provider(s), consider using system properties instead:

* `connectionPoolingAuthentication`
* `connectionPoolingInitSize`
* `connectionPoolingMaxSize`
* `connectionPoolingPrefSize`
* `connectionPoolingTimeout`
* `connectionPoolingProtocol`
* `connectionPoolingDebug`

For more details, see link:{adminguide_link}#_ldap_connection_pool[Configuring the connection pool].