code: def delete_records(keep=20):
      
      sql = "SELECT * from records where is_deleted<>1 ORDER BY id desc LIMIT -1 offset {}".format(keep)
      assert isinstance(g.db, sqlite3.Connection)
      c = g.db.cursor()
      c.execute(sql)
      rows = c.fetchall()
      for row in rows:
          name = row[1]
          xmind = join(app.config['UPLOAD_FOLDER'], name)
          xml = join(app.config['UPLOAD_FOLDER'], name[:-5] + 'xml')
  
          for f in [xmind, xml]:
              if exists(f):
                  os.remove(f)
  
          sql = 'UPDATE records SET is_deleted=1 WHERE id = ?'
          c.execute(sql, (row[0],))
          g.db.commit()
docs: Clean up files on server and mark the record as deleted