oracle foreign key primary key constraints performance tuning MTS IOT 9i block size backup rman corrupted column drop rename recovery controlfile backup clone architecture database archives export dump dmp duplicate rows extents segments fragmentation hot cold blobs migration tablespace locally managed redo undo new features rollback ora-1555 shrink free space user password link TNS tnsnames.ora listener java shutdown sequence

1. Moving a Table to a new Tablespace Administration Tips
Moving a Table
Moving a table from one tablespace to another is a piece of cake -provided you have
Oracle 8i. The command there is simply:
ALTER TABLE BLAH MOVE TABLESPACE XYZ;
The tablespace name in this command doesn't have to be a completely new tablespace: it's
perfectly permissible to move a table within a tablespace, and hence the name can
legitimately be the name of the tablespace it's already housed within.
There's only one slight word of warning with this command: the way it works is that a new
version of the table is created, under a temporary name, in the specified tablespace, and
then populated by selecting from the original table. When the populating exercise has
finished, the old version is dropped, and the new one simultaneously renamed as the old
one. For a split second, therefore, two versions of the table exist -and hence you need
sufficient disk space to accomodate those two versions. If this is 12Gb table you are
moving, that can be expensive!
Otherwise, there's not much to report on the 'move tablespace' command. It brings along
all constraints and permissions, so there's none of that to redefine. There is one slight
problem: all indexes on the table have got leaf nodes stuffed full of ROWIDs which point to
where the old table used to be. Now it's moved, those indexes are basically stuffed full of
worthless nonsense... hence the need to rebuild all indexes on a table that's been moved.
Suppose, however, you don't have the advantages of 8i and its "move tablespace" command.
How then do you do the deed?
Well, the simplest way would be to do a CTAS. That stands for "create table as select",
and refers to the fact that you could issue the following command:
CREATE TABLE NEW_EMP
TABLESPACE NEWONE
AS
SELECT * FROM OLD_EMP;
Only problem with this command is that you probably need to do it twice: assuming you
want the newly re-located table to be the same name as the original, you'd follow the
above command with a drop table old_emp; followed by a revamp of the earlier CTAS to
read 'create...old_emp as select * from new_emp'.
Copyright © Howard Rogers 2001 10/17/2001 Page 1 of 2

2. Moving a Table to a new Tablespace Administration Tips
But the real nasty with this technique is that the tables you create each time you run the
CTAS command are new tables. That means no-one has any rights on them, there are no
constraints defined for them, and no indexes exist for them. You'll need to re-grant all
permissions, re-create all constraints, and re-specify and re-create all indexes, too (now
isn't that upgrade to 8i looking attractive??!).
Another possibility presents itself: export the old table, then drop it. Alter the user so
that their quota on the original tablespace is zero, and also alter that user so that their
default tablespace is the one you want the new table created in. Import, you see, always
likes to create tables in a tablespace of exactly the same name as the one the table
originally came from. But if it can't create it there (and the quota of zero prevents that),
it will instead choose to create the table in whoever is running import's default tablespace.
This technique can get a bit fiddly, but has the advantage of re-creating all indexes,
constraints and re-granting all permissions. You'd have to remember to set the quotas and
default tablespace for the User involved back to what they were earlier, too.
At the end of the day, whichever version of Oracle you use, and whichever technique you
go for, moving tables is not a cheap exercise. Best house them correctly in the first place.
But if you have to do it, the 'move tablespace' option has the distinct advantages of ease of
implementation.
Copyright © Howard Rogers 2001 10/17/2001 Page 2 of 2