Repository size increases significantly after pull mirroring for forked projects

Incident: gitlab-com/gl-infra/production#19177 (closed)

Problem

The size of the repository increases every time after pull mirroring process is completed for forked repositories.

The issue may be caused by FetchRemoteRequest downloading objects repeatedly, as it cannot access objects from the forked object pool.

Proposal

Investigate the problem and discover the root cause.