Deleting a row from a table containing CLOB as one of the columns

Question

When i delete a row from a table which contains a CLOB (internal clob) i.e. CLOB or BLOB column, Will the CLOB data will also be deleted ? I understand that what exactly stored in the CLOB column is the clob locator which points to the actual data.
So, when I delete this row, the clob locator will be deleted, but will the actual data what this locator is pointing to is also deleted ??? if not what is the process to delete the data the locator is pointing to when the row containing the locator is deleted ? If this is not happening then the actual data might become an orphan data which nobody has access to, will automatic garbage cleaning occurs on a frequent intravels to delete unaddressed data residing on the database server ?
Thanks in advance for the help, can email me at [email protected] alternatively.
Regards,
Srinivasa C.

Answer 1

Michael,
Thanks very much for your inputs, here are the results i got when i tried the way you explained in your answer, the TRUNCATE command made the actual size back to normal, but the delete is not the same, so, how can i delete the data that a particular clob locator may point to ?
truncate would delete all the rows of the table, which might not serve my purpose, i would like to delete a row and also it's associated clob data from the database! is there anyway to do this ?
is there any limitation on the ool_sample size? i am basically a c++ programmer, i am looking for some function like FREE which would free the allocated memory to the clob once the locator is deleted.
your help is greatly appreciated - Thanks!
:-) Srini.
==========================
My Results:
==========================
SQL> create table sample (
2 id integer primary key,
3 the_data CLOB default empty_clob() )
4 lob (the_data) store as ool_sample;
Table created.
SQL> select segment_name, round(sum(bytes)/1024, 2) || 'K' as sotrage_consumed
2 from user_segments
3 where segment_name in ('SAMPLE', 'OOL_SAMPLE')
4 group by segment_name;
SEGMENT_NAME
SOTRAGE_CONSUMED
OOL_SAMPLE
20K
SAMPLE
10K
SQL> select count(*) from sample;
COUNT(*)
0
SQL> begin
2 for i in 1..1000
3 loop
4 insert into sample values (i, RPAD('some data', 4000) );
5 end loop;
6 end;
7 /
PL/SQL procedure successfully completed.
SQL> select segment_name, round(sum(bytes)/1024, 2) || 'K' as sotrage_consumed
2 from user_segments
3 where segment_name in ('SAMPLE', 'OOL_SAMPLE')
4 group by segment_name;
SEGMENT_NAME
SOTRAGE_CONSUMED
OOL_SAMPLE
6420K
SAMPLE
70K
SQL> delete sample;
1000 rows deleted.
SQL> select segment_name, round(sum(bytes)/1024, 2) || 'K' as sotrage_consumed
2 from user_segments
3 where segment_name in ('SAMPLE', 'OOL_SAMPLE')
4 group by segment_name;
SEGMENT_NAME
SOTRAGE_CONSUMED
OOL_SAMPLE
6420K
SAMPLE
70K
SQL> commit;
Commit complete.
SQL> select segment_name, round(sum(bytes)/1024, 2) || 'K' as sotrage_consumed
2 from user_segments
3 where segment_name in ('SAMPLE', 'OOL_SAMPLE')
4 group by segment_name;
SEGMENT_NAME
SOTRAGE_CONSUMED
OOL_SAMPLE
6420K
SAMPLE
70K
SQL> begin
2 for i in 1..1000
3 loop
4 insert into sample values (i, rpad('some data', 4000));
5 end loop;
6 end;
7 /
PL/SQL procedure successfully completed.
SQL> select segment_name, round(sum(bytes)/1024, 2) || 'K' as sotrage_consumed
2 from user_segments
3 where segment_name in ('SAMPLE', 'OOL_SAMPLE')
4 group by segment_name;
SEGMENT_NAME
SOTRAGE_CONSUMED
OOL_SAMPLE
9616K
SAMPLE
70K
SQL> truncate table sample;
Table truncated.
SQL> select segment_name, round(sum(bytes)/1024, 2) || 'K' as sotrage_consumed
2 from user_segments
3 where segment_name in ('SAMPLE', 'OOL_SAMPLE')
4 group by segment_name;
SEGMENT_NAME
SOTRAGE_CONSUMED
OOL_SAMPLE
20K
SAMPLE
10K