Question

I’ve been asked to free up the space assigned to BLOBS in Oracle. I will be extracting the data and then setting the BLOB to null to free up space.

According to the DBA this does not free up the space. SQL I am using is

UPDATE TABLENAME SET BLOB_FIELD_A = NULL

I did some googling and there is a function called EMPTY_BLOB(); No comment anywhere that it frees up the previously allocated space

Answer 1

the only way to shrink a segment in oracle is to MOVE/SHRINK it.

ie you have to run, once you’ve updated the lobs to null:

alter table b modify lob (c) (shrink space);

(available from 10.2 onwards)
or

alter table b move lob(c) store as (tablespace your_tablespace);