[CA-271014] Reduce Database calls in get_all_plugged_srs

Replace the database calls for each PBD to get its currently_attached with a single call using `get_refs_where` to get only the currently attached PBDs.

Signed-off-by: Callum McIntyre <[email protected]>

Author: Callum McIntyre

ocaml/xapi/helpers.ml

@@ -1012,8 +1012,8 @@ let i_am_srmaster ~__context ~sr =
   get_srmaster ~__context ~sr = get_localhost ~__context
 
 let get_all_plugged_srs ~__context =
-  let pbds = Db.PBD.get_all ~__context in
-  let pbds_plugged_in = List.filter (fun self -> Db.PBD.get_currently_attached ~__context ~self) pbds in
+  let pbds_plugged_in = Db.PBD.get_refs_where ~__context ~expr:(
+    Eq (Field "currently_attached", Literal "true")) in
   List.setify (List.map (fun self -> Db.PBD.get_SR ~__context ~self) pbds_plugged_in)
 
 let get_all_plugged_srs_local ~__context =