Fix memory issue on Infinity 0.6.15 (#12258)

### What problem does this PR solve?

1. Remove unused columns
2. Check the empty database
3. Switch on the order by expression

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

memory/utils/es_conn.py

@@ -228,14 +228,14 @@ class ESConnection(ESConnectionBase):
                 if str(res.get("timed_out", "")).lower() == "true":
                     raise Exception("Es Timeout.")
                 self.logger.debug(f"ESConnection.search {str(index_names)} res: " + str(res))
-                return res
+                return res, self.get_total(res)
             except ConnectionTimeout:
                 self.logger.exception("ES request timeout")
                 self._connect()
                 continue
             except NotFoundError as e:
                 self.logger.debug(f"ESConnection.search {str(index_names)} query: " + str(q) + str(e))
-                return None
+                return None, 0
             except Exception as e:
                 self.logger.exception(f"ESConnection.search {str(index_names)} query: " + str(q) + str(e))
                 raise e