HWM and Undo

Question

Hi ,
on 11g R2 on Win 2008,
my undo file is 5Gb and occupied only with 90 Mb. I want to resize to for example 4 Gb. It fails saying that there are users' data. Even if I just restarted database. I think that it is because of HWM.
How can I reduce it to be able to resize my undo file ?
Thanks.

Answer 1

check how much a tablespace shrinks wiith resize command.
column tablespace_name format a10
column file_name format a32
column file_mb format 9999990
column hwm_mb format 9999990
column used_mb format 9999990
column shrnk_mb format 9999990
break on report
compute sum of file_mb on report
compute sum of hwm_mb on report
compute sum of used_mb on report
compute sum of shrnk_mb on report
select a.*
, file_mb-hwm_mb shrnk_mb
from (
select /*+ rule */
a.tablespace_name,
a.file_name,
a.bytes/1024/1024 file_mb,
b.hwm*d.block_size/1024/1024 hwm_mb,
b.used*d.block_size/1024/1024 used_mb
from
dba_data_files a,
(select file_id,max(block_id+blocks-1) hwm,sum(blocks) used
from dba_extents
group by file_id) b,
dba_tablespaces d
where a.file_id = b.file_id
and a.tablespace_name = d.tablespace_name
) a
order by a.tablespace_name,a.file_name;