Blobs table size is increasing day by day

I have used Oracle database for a Drupal project. It is functioning very fine. But the problem is the blobs table size is increasing gradually and the site getting very slow.

I have checked the following

procedure write_blob(p_hash varchar2, p_blobid out number, p_blob out blob)
  as
  begin
    select blobid,
           content
      into p_blobid,
           p_blob
      from blobs
     where hash= p_hash
     for update;

  exception
   when no_data_found then
    insert into blobs (blobid,content,hash)
         values (seq_blobs.nextval,empty_blob,p_hash)
      returning blobid, content into p_blobid,
                                     p_blob;
  end;

Also I have checked the function to write in blobs table write_blob in database.inc for oracle project.

I manually deleted few records from blobs table, but then the sites gets broken.
I am not able to archive or flush the blobs table entry.

And one more issue is: below query is locking the database and CPU utilization is very high.
SELECT BLOBID, CONTENT FROM BLOBS WHERE HASH= :B1 FOR UPDATE

Please suggest on this regards.
Thanks.