@Override
  protected void serializeAttributes(DataOutputStream stream) throws IOException {
    PlanNodeType.SCHEMA_FETCH_MERGE.serialize(stream);
    ReadWriteIOUtils.write(storageGroupList.size(), stream);
    for (String storageGroup : storageGroupList) {
      ReadWriteIOUtils.write(storageGroup, stream);
    }
  }
This class defines the scanned result merge task of schema fetcher.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/plan/node/metadata/read/SchemaFetchMergeNode.java