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Don Burleson Blog 







reclaim storage space after update delete of lob blob column

Oracle Tips by Donald BurlesonApril 7, 2017

Question: What do I do to reclaim the spaced used when I shrink the size of a BLOB or LOB column within a table? 

We configured a scheduled job to update BLOB Column to EMPTY, This Job runs every night and update 30 days old rows.

   event_data = empty_blob();

Despite this we can see spike in tablespace usage,   How do I shrink the row lengths?

Answer:  The LOB/BLOB column still exists within the table blocks, and the data is still there.  It is only marked as unused.  To free up the space, use this command:

alter table
modify lob
(shrink space);

Remember, you must shrink lob or move, after updating column as null or empty_blob.  For a partitioned table, use this syntax:
alter table
   ev_log modify
(shrink space);

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