@Override
  public int execute() throws HiveException {
    Context generalContext = context.getContext();

    MergeFileWork mergeWork = getMergeFileWork(generalContext.getOpContext());
    Task<?> task = getTask(mergeWork);
    return executeTask(generalContext, task);
  }
Operation process of concatenating the files of a table/partition.
ql/src/java/org/apache/hadoop/hive/ql/ddl/table/storage/concatenate/AlterTableConcatenateOperation.java