@Override
  protected void doAlteration(Table table, Partition partition) throws HiveException {
    // Add the covert type
    String convertType = desc.getConvertSpec().getTargetType();
    ConversionFormats format = ConversionFormats.valueOf(convertType.toUpperCase());

    // Check the properties don't already exist, in that case we need not do any conversion
    validatePropertiesAlreadyExist(format, table.getParameters());

    // Add the conversion related table properties.
    table.getParameters().putAll(format.properties());

    // Add any additional table properties, if specified with the convert command.
    if (desc.getConvertSpec().getTblProperties() != null) {
      table.getParameters().putAll(desc.getConvertSpec().getTblProperties());
    }
  }
Operation process of ALTER TABLE ... CONVERT command
ql/src/java/org/apache/hadoop/hive/ql/ddl/table/convert/AlterTableConvertOperation.java