Ref Guide: first pass at 8.3 upgrade notes

solr/solr-ref-guide/src/solr-upgrade-notes.adoc

@@ -31,6 +31,33 @@ Detailed steps for upgrading a Solr cluster are in the section <<upgrading-a-sol
 
 If you are upgrading from 7.x, see the section <<Upgrading from 7.x Releases>> below.
 
+=== Solr 8.3
+
+See the 8.3 Release Notes for an overview of the main new features of Solr 8.3.
+
+When upgrading to 8.3.x users should be aware of the following major changes from 8.2.
+
+*JWT Authentication*
+
+JWT Authentication now supports multiple identity providers.
+To allow this, the parameter `jwkUrl` has been deprecated and replaced with `jwksUrl`.
+Implementations using `jwkUrl` will continue to work as normal, but users
+ should plan to transition their configurations to use `jwksUrl` instead as
+ soon as feasible.
+
+*Caches*
+
+* Solr has a new cache implementation, `CaffeineCache`, which is now recommended over other caches. This cache is expected to generally provide most users lower memory footprint, higher hit ratio, and better multi-threaded performance.
++
+Since caching has a direct impact on the performance of your Solr
+ implementation, before switching to any new cache implementation in
+ production, take care to test for your environment and traffic patterns so
+ you fully understand the ramifications of the change.
+
+* A new parameter, `maxIdleTime`, allows automatic eviction of cache items that have not been used in the defined amount of time. This allows the cache to release some memory and should aid those who want or need to fine-tune their caches.
+
+See the section <<query-settings-in-solrconfig.adoc#query-settings-in-solrconfig,Query Settings in SolrConfig>> for more details about these and other cache options and parameters.
+
 === Solr 8.2
 
 See the https://cwiki.apache.org/confluence/display/SOLR/ReleaseNote82[8.2 Release Notes] for an overview of the main new features of Solr 8.2.