Crucible reports 'Changeset not found' when reviewers attempt to view changes in the code review
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*Except Fisheye and Crucible
Summary
Crucible reports 'Changeset not found' when reviewers attempt to view changes in code review. 
The issue is observed when the branches used in a review are deleted in the (Source Code Management) SCM server and the git repository is reindexed in Fisheye.
Environment
Fisheye Crucible - 4.8.9
Repository type - Git
Cause
This is expected behavior. In Git, branches are pointers to tips of commit-tree branches. Git by default stores only those commits which are accessible by a branch. In other words, if you delete the branch and there’s no other branch pointing to that commit, the commits from that branch become inaccessible. Fisheye when scanning a repository can access only those commits which are present in a repository, and accessible via branches. Therefore, if a branch is removed, thus ‘deleted’ commits, and next triggered a full repository reindex in Fisheye, there’s no way Fisheye can access the changeset.
Solution
Enable file storage revision for the project as documented in Storing all revisions under review.
By enabling the "Store the contents of files in reviews" option for the project, it allows you to be able to view that file content whether or not the repository is online or accessible to Crucible. It also creates an enhanced audit trail should you require it, saving the review content regardless of whether or not it is deleted or lost from the repository.