void checkAndUpdateSafeDeletedSearchIndex() {
    if (configuration.isEmpty()) {
      logger.error(
          "Configuration is empty, which is unexpected. Safe deleted search index won't be updated this time.");
    } else if (configuration.size() == 1) {
      consensusReqReader.setSafelyDeletedSearchIndex(Long.MAX_VALUE);
    } else {
      consensusReqReader.setSafelyDeletedSearchIndex(getMinFlushedSyncIndex());
    }
  }
If there is only one replica, set it to Long.MAX_VALUE. If there are multiple replicas, get the
latest SafelyDeletedSearchIndex again. This enables wal to be deleted in a timely manner.
iotdb-core/consensus/src/main/java/org/apache/iotdb/consensus/iot/IoTConsensusServerImpl.java