History rewrites are non-fast-forward updates of remote refs and associated objects. History rewrites happen when a branch in a remote repository gets deleted, previously pushed commits get amended or filtered and forcefully re-pushed, or a remote branch/tag is pointed to an entirely different commit history.
History may get rewritten without leaving any trace of the previous state. Sometimes this behavior may be wanted - for example, in the case of removing code violating intellectual property, removing mistakenly committed large binary files or removing merged feature branches. The TeamForge Git integration therefore does not disable the history rewrite feature, but instead enables it for SCM Administrators alone. However, since rewriting history might be easily abused and result in accidental data loss, we've introduced the History Protection feature as a safety net and necessity for ensuring proper audit compliance.
History protection archives rewritten changes and keeps backups of deleted branches. If history changes occur, an immutable backup ref is created in the remote repository, notification emails sent to all members of the Gerrit Administrators group, and an event logged in the audit log. The backed up ref can be restored into a new branch with any Git client (without needing physical file access to the Gerrit server). Gerrit site administrators can still decide to remove selected backup refs permanently.