一次导出expdp遭遇ora-01555

无论在全部导出还是单表导出时，均遇到以下报错：

. . exported "[owner]"."[TABLE_NAME]"           142.5 MB 3067166 rows
ORA-31693: Table data object "[owner]"."[TABLE_NAME]" failed to load/unload and is being skipped due to error:
ORA-02354: error in exporting/importing data
ORA-01555: snapshot too old: rollback segment number  with name "" too small
ORA-22924: snapshot too old

尝试调整undo_retention，发现表也存在lob字段，调整lob的retetion时间：

select table_name,column_name,pctversion,retention from dba_lobs where table_name='[TABLE_NAME]';
#修改语句：
ALTER TABLE [TABLE_NAME] MODIFY LOB([COLUMN_NAME])(retention);

但故障依旧。
后经过继续网上的查找，是表记录出错，通过以下方法排除问题：

1、查看该表的lob的信息：
select table_name,column_name,pctversion,retention from dba_lobs where table_name='[TABLE_NAME]';
2、创建临时表保存出错的记录：
create table corrupt_lobs_wfcaserun (corrupt_rowid rowid);

执行以下存储过程：

declare
error_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;
begin
for cursor_lob in (select rowid r, [LOB字段] from [OWNER].[TABLE_NAME]) loop
begin
num := dbms_lob.instr(cursor_lob.[LOB字段], hextoraw('889911'));
exception
when error_1578 then
insert into corrupt_lobs_wfcaserun values (cursor_lob.r);
commit;
when error_1555 then
insert into corrupt_lobs_wfcaserun values (cursor_lob.r);
commit;
when error_22922 then
insert into corrupt_lobs_wfcaserun values (cursor_lob.r);
commit;
end;
end loop;
end;
/

查看损坏的记录，并删除：

select * from corrupt_lobs_wfcaserun;

delete from [OWNER].[TABLE_NAME] where rowid in (select corrupt_rowid from corrupt_lobs_wfcaserun);
COMMIT;

还有一种方法是清除记录中的lob的内容（未测试）：

update [OWNER].[TABLE_NAME] set [字段]=empty_clob() where rowid in (select corrupt_rowid from corrupt_lobs_wfcaserun);

再重新导出后，正常，特此记录。