In rare cases, the fuzzy cluster migration test detected missing keys. It turns out that the missing keys were skipped at the source side due to contention:
The OnDbChange callback registered and got a snapshot_id
It then blocked on a mutex, and could not add itself to the list of callbacks
When the mutex was released, it registered, but it missed all changes that happened between registering (snapshot_id) and the moment it registered
In rare cases, the fuzzy cluster migration test detected missing keys. It turns out that the missing keys were skipped at the source side due to contention:
snapshot_idsnapshot_id) and the moment it registered