@SuppressFBWarnings(value = "EI_EXPOSE_REP", justification = "intended")
  public Map<String, SnapshotContext> getTableSnapshots() {
    return tableSnapshots;
  }
Gets the snapshotIds of the MV source tables when the MV was created/last rebuilt
@return {@link Map} of snapshotIds where the key is the fully qualified name of the table and the
values is the {@link String} representation of snapshotId or null if all tables are native ACID
storage-api/src/java/org/apache/hadoop/hive/common/MaterializationSnapshot.java