== Server Cache Configuration

{{book.project.name}} has two types of caches.  One type of cache sits in front of the database to decrease load on the DB
and to increase overall response times by keeping data in memory.  Realm, client, role, and user metadata is kept in this cache.
The caching for this data is stored in something called an invalidation cache.  Invalidation caches do not use replication.
Instead, they only keep copies locally and if the entry is updated an invalidation message is sent to the rest of the cluster
and the entry is evicted.  This greatly reduces network traffic, makes things efficient, and avoids transmitting sensitive
metadata over the ire.

The second type of cache handles managing user sessions, offline tokens, and keeping track of login failures so that the
server can detect password phishing and other attacks.  The data held in these caches is temporary, in memory only,
but is possibly replicated across the cluster.

This chapter discusses some configuration options for these caches for both clustered a non-clustered deployments.

Note:  More advanced configuration of these caches can be found in link:{{book.caching.admindoc.link}}[{{book.caching.admindoc.name}}]