Current behavior

Pull request rescoping updates the Git refs of all pull requests affected in a rescope operation. While updating each pull request's refs, a cluster-level lock for the pull request has to be acquired. This lock is also acquired for various other operations and can delay rescope processing.

Suggested improvement

Bitbucket only tracks the 'from-ref' of a pull request in Git, the 'to-ref' is not stored. Updating the pull request refs could be limited to only those pull requests that had their 'from-ref' updated.

Most large rescope operations occur when the default branch of a repository has been updated. Under the assumption that most pull requests in a repository target the default branch, as in, their 'to-ref' points to the default branch, a large portion of those pull requests could be rescoped without having to update their refs and therefore avoid cluster wide locking.