@Override
  public Set<StoreKey> findMissingKeys(List<StoreKey> keys) throws StoreException {
    Set<StoreKey> keysMissing = new HashSet<>();
    for (StoreKey key : keys) {
      boolean found = false;
      for (MessageInfo messageInfo : messageInfos) {
        if (messageInfo.getStoreKey().equals(key)) {
          found = true;
          break;
        }
      }
      if (!found) {
        keysMissing.add(key);
      }
    }
    return keysMissing;
  }
Log that stores all data in memory.
ambry-replication/src/test/java/com/github/ambry/replication/InMemoryStore.java