In 8.x branch, the default and example configsets include LRUCache and FastLRUCache as the implementation for the various caches.
<filterCache class="solr.FastLRUCache" size="512" initialSize="512" autowarmCount="0"/>
Those implementations are deprecated. We should remove the attribute completely and let the default take over (as it's in master), this should make upgrading configsets easier:
- links to