CP-49045: optimize database uuid lookup: use index

An index (map) has already been created, but it was only used to lookup Refs, not UUIDs.
A latent bug in the UUID index was fixed in a previous commit.

Signed-off-by: Edwin Török <edwin.torok@citrix.com>

Author: edwintorok

ocaml/database/db_cache_impl.ml

@@ -277,21 +277,13 @@ let read_field_where' conv t rcd =
 let read_field_where t rcd = read_field_where' Fun.id t rcd
 
 let db_get_by_uuid t tbl uuid_val =
-  match
-    read_field_where' Schema.CachedValue.string_of t
-      {
-        table= tbl
-      ; return= Db_names.ref
-      ; where_field= Db_names.uuid
-      ; where_value= uuid_val
-      }
-  with
-  | [] ->
-      raise (Read_missing_uuid (tbl, "", uuid_val))
-  | [r] ->
+  let db = get_database t in
+  match Database.lookup_uuid uuid_val db with
+  | Some (tbl', r) when String.equal tbl tbl' ->
       r
   | _ ->
-      raise (Too_many_values (tbl, "", uuid_val))
+      (* we didn't find the UUID, or it belonged to another table *)
+      raise (Read_missing_uuid (tbl, "", uuid_val))
 
 let db_get_by_uuid_opt t tbl uuid_val =
   match

ocaml/database/db_cache_types.ml

@@ -508,6 +508,8 @@ module Database = struct
 
   let lookup_key key db = KeyMap.find_opt (Ref key) db.keymap
 
+  let lookup_uuid key db = KeyMap.find_opt (Uuid key) db.keymap
+
   let make schema =
     {
       tables= TableSet.empty

ocaml/database/db_cache_types.mli

@@ -195,6 +195,8 @@ module Database : sig
 
   val lookup_key : string -> t -> (string * string) option
 
+  val lookup_uuid : string -> t -> (string * string) option
+
   val reindex : t -> t
 
   val register_callback : string -> (update -> t -> unit) -> t -> t