RE: ALTER ROLLBACK SEGMENT rbs SHRINK

From: Johnston, Tim <TJohnston_at_quallaby.com>
Date: Wed, 30 Jan 2002 13:03:35 -0800
Message-ID: <F001.0040109D.20020130123503@fatcity.com>

Ok... I've ran this test case on both a 8.1.6.0 and a 8.1.7.3 database... I've ran it with both public and private rollback segments (just in case)... I've looked at rssize in v$rollstat and sum(bytes) from dba_segments... And, in all cases, it allows me to shrink the segment to less then both optimal and min_extents*extent_size even though optimal=min_extents*extent_size... Is there something wrong in the test case? Has anyone ran this on one of their test databases? I'm confused since the test case seems straight forward... The way I read, it allows me to perform the shrink and the resulting segment is actually the size I specify... Am I doing something stupid in the test case?

Thanks
Tim

PS - Here is the test case again...

column segment_name format a30
create public rollback segment tim tablespace rbs storage ( initial 1M next 1M minextents 20 maxextents 100 optimal 20M ); alter rollback segment tim online;
select segment_name, min_extents, initial_extent, next_extent   from dba_segments
 where segment_name = 'TIM';
select rs.extents, rs.rssize/1048576 , rs.optsize/1048576   from dba_rollback_segs drs,

       v$rollstat rs
 where drs.segment_name = 'TIM'
   and drs.segment_id = rs.usn;
alter rollback segment TIM shrink to 10M; select segment_name, min_extents, initial_extent, next_extent   from dba_segments
 where segment_name = 'TIM';
select rs.extents, rs.rssize, rs.optsize   from dba_rollback_segs drs,

       v$rollstat rs
 where drs.segment_name = 'TIM'
   and drs.segment_id = rs.usn;
alter rollback segment tim offline;
drop rollback segment tim;

-----Original Message-----
Sent: Wednesday, January 30, 2002 2:31 PM To: Multiple recipients of list ORACLE-L

Um... Must be version differences... Here is a test case I ran on my 8.1.7.3 machine...

SQL> create public rollback segment tim tablespace rbs storage ( initial 1M next 1M minextents 20 maxextents 100 optimal 20M );

Rollback segment created.

SQL> alter rollback segment tim online;

Rollback segment altered.

SQL> select segment_name, min_extents, initial_extent, next_extent   2 from dba_segments
  3 where segment_name = 'TIM';

SEGMENT_NAME                   MIN_EXTENTS INITIAL_EXTENT NEXT_EXTENT
------------------------------ ----------- -------------- -----------
TIM                                     20        1048576     1048576

SQL> select rs.extents, rs.rssize/1048576 , rs.optsize/1048576   2 from dba_rollback_segs drs,
  3 v$rollstat rs
  4 where drs.segment_name = 'TIM'
  5 and drs.segment_id = rs.usn;

   EXTENTS RS.RSSIZE/1048576 RS.OPTSIZE/1048576

---------- ----------------- ------------------
        20         20.296875                 20

SQL> alter rollback segment TIM shrink to 10M;

Rollback segment altered.

SQL> select segment_name, min_extents, initial_extent, next_extent   2 from dba_segments
  3 where segment_name = 'TIM';

SEGMENT_NAME                   MIN_EXTENTS INITIAL_EXTENT NEXT_EXTENT
------------------------------ ----------- -------------- -----------
TIM                                     20        1048576     1048576

SQL> select rs.extents, rs.rssize, rs.optsize   2 from dba_rollback_segs drs,
  3 v$rollstat rs
  4 where drs.segment_name = 'TIM'
  5 and drs.segment_id = rs.usn;

   EXTENTS RSSIZE OPTSIZE
---------- ---------- ----------

        10 10633216 20971520

SQL> alter rollback segment tim offline;

Rollback segment altered.

SQL> drop rollback segment tim;

Rollback segment dropped.

SQL> What version is your test running on?

Tim

PS - Here is my test case if you want to run it...

column segment_name format a30
create public rollback segment tim tablespace rbs storage ( initial 1M next 1M minextents 20 maxextents 100 optimal 20M ); alter rollback segment tim online;
select segment_name, min_extents, initial_extent, next_extent   from dba_segments
 where segment_name = 'TIM';
select rs.extents, rs.rssize/1048576 , rs.optsize/1048576   from dba_rollback_segs drs,

       v$rollstat rs
 where drs.segment_name = 'TIM'
   and drs.segment_id = rs.usn;
alter rollback segment TIM shrink to 10M; select segment_name, min_extents, initial_extent, next_extent   from dba_segments
 where segment_name = 'TIM';
select rs.extents, rs.rssize, rs.optsize   from dba_rollback_segs drs,

       v$rollstat rs
 where drs.segment_name = 'TIM'
   and drs.segment_id = rs.usn;
alter rollback segment tim offline;
drop rollback segment tim;

-----Original Message-----
Sent: Wednesday, January 30, 2002 2:17 PM To: Multiple recipients of list ORACLE-L

testing....

if the initial extent*min_extents is less than the optimal, yes you can shrink below optimal.

if initial*minextents = optimal, you can execute an alter rollback segment statement that lists a shrink size that is less than optimal AND less than initial*minextents and it will not fail. But if you LOOK at the size it shrinks to, it's initial*minextents.

so you can "kinda" shrink below optimal, the statement won't fail, but Oracle will ignore the number you give it.
--

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--

Author: Johnston, Tim
  INET: TJohnston_at_quallaby.com

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