private boolean isPersistedStore(String storeName) {
    return Optional.ofNullable(stores.get(storeName))
        .map(StorageEngine::getStoreProperties)
        .map(StoreProperties::isPersistedToDisk)
        .orElse(false);
  }
Gets the side input SSP offsets for all stores from their local offset files.

@return a {@link Map} of {@link SystemStreamPartition} to offset in the offset files.
samza-core/src/main/java/org/apache/samza/storage/TaskSideInputStorageManager.java