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
assert shardRouting.initializing() : "can only start recovery on initializing shard";
        StoreRecovery storeRecovery = new StoreRecovery(shardId, logger);
        storeRecovery.recoverFromStore(this, listener);
    }
    public void restoreFromRepository(Repository repository, ActionListener<Boolean> listener) {
        try {
            assert shardRouting.primary() : "recover from store only makes sense if the shard is a primary shard";
            assert recoveryState.getRecoverySource().getType() == RecoverySource.Type.SNAPSHOT
                : "invalid recovery type: " + recoveryState.getRecoverySource();
            StoreRecovery storeRecovery = new StoreRecovery(shardId, logger);
            storeRecovery.recoverFromRepository(this, repository, listener);
        } catch (Exception e) {
            listener.onFailure(e);
        }
    }
    /**
     * Tests whether or not the engine should be flushed periodically.
     * This test is based on the current size of the translog compared to the configured flush threshold size.
     *
     * @return {@code true} if the engine should be flushed
     */
    boolean shouldPeriodicallyFlush() {
        final Engine engine = getEngineOrNull();
        if (engine != null) {
            try {
                return engine.shouldPeriodicallyFlush();
            } catch (final AlreadyClosedException e) {
                
            }
        }