Updated the section of the guide describing the new Solr optimization

feature flags. #10554

Author: landreev

doc/sphinx-guides/source/installation/config.rst

@@ -3269,7 +3269,10 @@ please find all known feature flags below. Any of these flags can be activated u
       - Enables API authentication via session cookie (JSESSIONID). **Caution: Enabling this feature flag exposes the installation to CSRF risks!** We expect this feature flag to be temporary (only used by frontend developers, see `#9063 <https://github.com/IQSS/dataverse/issues/9063>`_) and for the feature to be removed in the future.
       - ``Off``
     * - avoid-expensive-solr-join
-      - Changes the way Solr queries are constructed for guest (unauthenticated) users. From a search perspective, it disables :doc:`IP Groups </admin/ip-groups>` (collections, datasets, and files will not be discoverable) but it removes an expensive Solr join for the most common users, which are guests, to help improve overall performance. After turning on this feature, you must perform a full reindex. See :doc:`/admin/solr-search-index`.
+      - Changes the way Solr queries are constructed for public content (published Collections, Datasets and Files). It removes a very expensive Solr join on all such documents, improving overall performance, especially for large instances under heavy load. Before this feature flag is enabled, the corresponding indexing feature (see next feature flag) must be turned on and a full reindex performed (otherwise public objects are not going to be showin in search results). See :doc:`/admin/solr-search-index` . 
+      - ``Off``
+    * - add-publicobject-solr-field
+      - Adds an extra boolean field `PublicObject_b:true` for public content (published Collections, Datasets and Files). Once reindexed with these fields, we can rely on it to remove a very expensive Solr join on all such documents in solr queries, significantly improving overall performance (by enabling the feature flag above, `avoid-expensive-solr-join`. These two flags are made separate, so that an instance can reindex their holdings before enabling the optimization in searches, thus avoiding having their public objects temporarily disappear from search results while the reindexing is in progress. 
       - ``Off``
 
 **Note:** Feature flags can be set via any `supported MicroProfile Config API source`_, e.g. the environment variable