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/index/shard/IndexShard.java
engine.rollTranslogGeneration();
    }
    public void forceMerge(ForceMergeRequest forceMerge) throws IOException {
        verifyActive();
        if (logger.isTraceEnabled()) {
            logger.trace("force merge with {}", forceMerge);
        }
        Engine engine = getEngine();
        engine.forceMerge(forceMerge.flush(), forceMerge.maxNumSegments(), forceMerge.onlyExpungeDeletes(), forceMerge.forceMergeUUID());
    }
    /**
     * Creates a new {@link IndexCommit} snapshot from the currently running engine. All resources referenced by this
     * commit won't be freed until the commit / snapshot is closed.
     *
     * @param flushFirst <code>true</code> if the index should first be flushed to disk / a low level lucene commit should be executed
     */
    public Engine.IndexCommitRef acquireLastIndexCommit(boolean flushFirst) throws EngineException {
        final IndexShardState state = this.state; 
        
        if (state == IndexShardState.STARTED || state == IndexShardState.CLOSED) {
            return getEngine().acquireLastIndexCommit(flushFirst);
        } else {
            throw new IllegalIndexShardStateException(shardId, state, "snapshot is not allowed");
        }
    }
    /**
     * Acquires the {@link IndexCommit} which should be included in a snapshot.
     */
    public Engine.IndexCommitRef acquireIndexCommitForSnapshot() throws EngineException {
        final IndexShardState state = this.state;