清理大表历史数据
    通过将非分区表Online Redefinition转换为以删除条件为Range范围分区的Partition-ed Table，再直接Truncate Partiton的方法来加速历史数据的清理，
    同时又不影响业务的在线。
    create table order_history as select * from dba_objects;
    select count(*) from order_history;
    select count(*) from order_history where created < sysdate-365;

  COUNT(*)
    ———-
         49983
    收集统计信息
    exec dbms_stats.gather_table_stats('SCOTT','ORDER_HISTORY');

create table order_history_int(
     OWNER                                              VARCHAR2(30),
     OBJECT_NAME                                        VARCHAR2(128),
     SUBOBJECT_NAME                                     VARCHAR2(30),
     OBJECT_ID                                          NUMBER,
     DATA_OBJECT_ID                                     NUMBER,
     OBJECT_TYPE                                        VARCHAR2(19),
     CREATED                                            DATE,
     LAST_DDL_TIME                                      DATE,
     TIMESTAMP                                          VARCHAR2(19),
     STATUS                                             VARCHAR2(7),
     TEMPORARY                                          VARCHAR2(1),
     GENERATED                                          VARCHAR2(1),
     SECONDARY                                          VARCHAR2(1))
    partition by range(created)
    ( partition p1 values less than (to_date('2010-01-01','YYYY-MM-DD')) tablespace users,
      partition p2 values less than (to_date('2011-01-01','YYYY-MM-DD')) tablespace users,
      partition p3 values less than (to_date('2012-01-01','YYYY-MM-DD')) tablespace users,
      partition p4 values less than (to_date('2013-01-01','YYYY-MM-DD')) tablespace users,
      partition p5 values less than (maxvalue) tablespace users);
      
    begin
      dbms_redefinition.can_redef_table(uname        => 'SCOTT',
                                        tname        => 'ORDER_HISTORY',
                                        options_flag => DBMS_REDEFINITION.CONS_USE_ROWID);
    end;
    /

begin
    DBMS_REDEFINITION.START_REDEF_TABLE(uname        => 'SCOTT',
                                          orig_table   => 'ORDER_HISTORY',
                                          int_table    => 'ORDER_HISTORY_INT',
                                          options_flag => DBMS_REDEFINITION.cons_use_rowid);
    end;
    /

SQL> select count(*) from ORDER_HISTORY_INT;

  COUNT(*)
    ———-
         50731

DECLARE
      num_errors PLS_INTEGER;
    BEGIN
      DBMS_REDEFINITION.COPY_TABLE_DEPENDENTS(uname            => 'SCOTT',
                                              orig_table       => 'ORDER_HISTORY',
                                              int_table        => 'ORDER_HISTORY_INT',
                                              copy_indexes     => 0,
                                              copy_triggers    => TRUE,
                                              copy_constraints => FALSE,
                                              copy_privileges  => TRUE,
                                              ignore_errors    => FALSE,
                                              num_errors       => num_errors,
                                              copy_statistics  => TRUE);
    END;
    /

begin
      dbms_redefinition.finish_redef_table(uname      => 'SCOTT',
                                           orig_table => 'ORDER_HISTORY',
                                           int_table  => 'ORDER_HISTORY_INT');
    end;
    /

alter table ORDER_HISTORY truncate partition p1;
    alter table ORDER_HISTORY truncate partition p2;
    alter table ORDER_HISTORY truncate partition p3;
    SQL> select count(*) from ORDER_HISTORY;

  COUNT(*)
    ———-
           748