Performance issues for saving large groups

We noticed XWiki instances becoming slow because of saving large groups (different to XWikiAllGroup that can be set implicit) that are mapped from a third-party authentication source (like LDAP, OpenID, Trusted Authentication framework …)
An XWiki instance with performance issues related to large groups can be diagnosed as such :

• Slowness from users when they attempt to login. Once the users have logged-in, the navigation is better.
• The XWiki instance contains one or multiple groups (different than XWikiAllGroup) that have a lot of members.
• Large groups identified above have a large history : when clicking on the “History” tab of the group, you will see 1000+ versions in the group history.