We saw a case where the recovery stats reported `recovered_bytes` greater than `length_in_bytes` for one file:

```
GET /_recovery?detailed

200 OK
...
{
  "name": "_buk.fdt",
  "length_in_bytes": 26891307173,
  "reused": false,
  "recovered_in_bytes": 35324928266,
  "recovered_from_snapshot_in_bytes": 8433621093
}
...
```

NB `35324928266 == 26891307173 + 8433621093`

This causes Elasticsearch to compute a negative value for the reserved space on the target node of this recovery, which prevents stats APIs from working. This appears to be caused by a network-level failure which triggers a retry without first cancelling an ongoing download of a different file with the same name from the snapshot repository.

---

### Workaround

Restart the target node to clear these stats.
server/src/main/java/org/elasticsearch/indices/recovery/RecoveryState.java
out.writeVInt(totalLocal);
            }
        }
        public synchronized void reset() {
            super.reset();
            recovered = 0;
            total = UNKNOWN;
            totalOnStart = UNKNOWN;
            totalLocal = UNKNOWN;
        }
        public synchronized void incrementRecoveredOperations() {
            recovered++;
            assert total == UNKNOWN || total >= recovered
                : "total, if known, should be > recovered. total [" + total + "], recovered [" + recovered + "]";
        }
        public synchronized void incrementRecoveredOperations(int ops) {
            recovered += ops;
            assert total == UNKNOWN || total >= recovered
                : "total, if known, should be > recovered. total [" + total + "], recovered [" + recovered + "]";
        }
        public synchronized void decrementRecoveredOperations(int ops) {
            recovered -= ops;
            assert recovered >= 0
                : "recovered operations must be non-negative. Because [" + recovered + "] after decrementing [" + ops + "]";
            assert total == UNKNOWN || total >= recovered
                : "total, if known, should be > recovered. total [" + total + "], recovered [" + recovered + "]";
        }
        /**
         * returns the total number of translog operations recovered so far
         */