@Override
  public Set<StoreKey> findMissingKeys(List<StoreKey> keys) throws StoreException {
    // Keys may be missing if we are here, we are here to find out
    try {
      Set<StoreKey> missingKeys = new HashSet<>();
      for (StoreKey key : keys) {
        if (!cloudDestination.doesBlobExist((BlobId) key)) {
          missingKeys.add(key);
        }
      }
      return missingKeys;
    } catch (Throwable e) {
      throw new StoreException(e.getMessage(), StoreErrorCodes.IOError);
    }
  }
Find missing keys
@param keys The list of keys that need to be checked for existence
@return
@throws StoreException
ambry-cloud/src/main/java/com/github/ambry/cloud/CloudBlobStore.java