–expdp导出某一张表的时候总是出现如下报错

ORA-02354: error in exporting/importing data
ORA-01555: snapshot too old: rollback segment number  with name "" too small
ORA-22924: snapshot too old

–在导出过程中观察undo的使用情况，发现并未占用多少undo，undo空间其实是够用的
随后查看表的字段，发现有lob字段，很有可能是lob字段损坏导致的

–创建一张临时表，保存损坏的表记录信息

create table corrupt_lobs_wfcaserun (corrupt_rowid rowid);

–执行下面的存储过程（LOB字段写导出表的lob字段，tablename写表名）

declareerror_1578  exception;error_1555  exception;error_22922 exception;pragma exception_init(error_1578, -1578);pragma exception_init(error_1555, -1555);pragma exception_init(error_22922, -22922);num number;
beginfor cursor_lob in (select rowid r, LOB字段 from tablename) loopbeginnum := dbms_lob.instr(cursor_lob.LOB字段, hextoraw('889911'));exceptionwhen error_1578 theninsert into corrupt_lobs_wfcaserun values (cursor_lob.r);commit;when error_1555 theninsert into corrupt_lobs_wfcaserun values (cursor_lob.r);commit;when error_22922 theninsert into corrupt_lobs_wfcaserun values (cursor_lob.r);commit;end;end loop;
end;
/

–如果有损坏的记录，会自动记录到刚刚创建的临时表当中

select * from corrupt_lobs_wfcaserun;

–表里记录了损坏字段的rowid，根据rowid对损坏的记录进行删除或者是更新

delete from tablename where rowid ='';
update tablename set lob字段='' where rowid ='';

–损坏的记录处理后再重新进行exppd导出，终于正常