Is Segment Advisor Inaccurate?

Question

Based on a few tests I've been running, I haven't been able to reproduce space savings that Segment Advisor reports. For example, the top segment in terms of space reclamation that Segement Advisor lists has *1019.16MB* of reclaimable space. When I execute the commands:
alter table <owner>.<table_name> enable row movement;
alter table <owner>.<table_name> shrink space;
... the space savings listed in the tablespace before and after are only a difference of *138MB*.
Why the difference? This has occurred for every segment that I have executed the statements above for; the space savings are considerably less than Segment Advisor claims.
Anybody else experiencing this?

Answer 1

I've experienced something similar with the versions I use: 10.2.0.1 and 10.2.0.4 (linux 32 bits). I've found that executing "alter table ... shrink space" twice finally releases the space.
Segment Advisor:
Tablespace: Users, Segment: Scott.T,
Reclaimable space: 19.39,
Allocated Space:27.00,
Used space: 7.61,
Segment Type: Table
SYS@orcl > execute show_space('T','SCOTT');
Unformatted Blocks .....               0
FS1 Blocks (0-25)  .....               0
FS2 Blocks (25-50) .....               7
FS3 Blocks (50-75) .....               6
FS4 Blocks (75-100).....           2,718
Full Blocks        .....             663
Total Blocks............           3,456
Total Bytes.............      28,311,552
Total MBytes............              27
Unused Blocks...........               0
Unused Bytes............               0
Last Used Ext FileId....               4
Last Used Ext BlockId...           3,465
Last Used Block.........             128
PL/SQL procedure successfully completed.
SYS@orcl > alter table scott.t shrink space;
Table altered.
SYS@orcl > execute show_space('T','SCOTT');
Unformatted Blocks .....               0
FS1 Blocks (0-25)  .....               0
FS2 Blocks (25-50) .....               1
FS3 Blocks (50-75) .....               0
FS4 Blocks (75-100).....           2,724
Full Blocks        .....             669
Total Blocks............           3,456
Total Bytes.............      28,311,552
Total MBytes............              27
Unused Blocks...........               0
Unused Bytes............               0
Last Used Ext FileId....               4
Last Used Ext BlockId...           3,465
Last Used Block.........             128
PL/SQL procedure successfully completed.
SYS@orcl > alter table scott.t shrink space;
Table altered.
SYS@orcl >  execute show_space('T','SCOTT');
Unformatted Blocks .....               0
FS1 Blocks (0-25)  .....             193
FS2 Blocks (25-50) .....               1
FS3 Blocks (50-75) .....               0
FS4 Blocks (75-100).....               0
Full Blocks        .....             476
Total Blocks............             696
Total Bytes.............       5,701,632
Total MBytes............               5
Unused Blocks...........               6
Unused Bytes............          49,152
Last Used Ext FileId....               4
Last Used Ext BlockId...             777
Last Used Block.........              50
PL/SQL procedure successfully completed.Initial size: 3456 blocks
Final size : 696 blocks -- but after two consecutive shrinks
Space Saving= 21MB, Segment Advisor predicted 19.39MB.
Enrique