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CP-40669: Restore database should not require ref as the first #4781

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Aug 30, 2022
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CP-40669: Restore database should not require ref as the first #4781

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15 changes: 12 additions & 3 deletions ocaml/database/db_xml.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -146,15 +146,24 @@ module From = struct
f acc
| (_, "table"), [((_, "name"), tblname)] ->
f (tableset, Table.empty, tblname, manifest)
| (_, "row"), ((_, "ref"), rf) :: rest ->
(* Remove any other duplicate "ref"s which might have sneaked in there *)
let rest = List.filter (fun ((_, k), _) -> k <> "ref") rest in
| (_, "row"), rest ->
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Altogether, this code is traversing lists multiple times and is inefficient if these lists are long. But that problem is already pre-existing.

The problem at hand is to find the first "ref" entry and to ignore the others. The solution is to split the list based on the key and we expect to find at least one entry. I think the code achieving this could be kept closer together - a sketch is below:

let ref, rest =
  match List.partition (fun ((_, k) -> k = "ref")) rest with
  | r::_, rest -> r,rest
  | [] -> raise ...

let ref_l, rest =
List.partition (fun ((_, k), _) -> k = "ref") rest
in

let ctime_l, rest =
List.partition (fun ((_, k), _) -> k = "__ctime") rest
in
let mtime_l, rest =
List.partition (fun ((_, k), _) -> k = "__mtime") rest
in
let rf =
match ref_l with
| (_, ref) :: _ ->
ref (* Pick up the first ref and ignore others *)
| [] ->
raise (Unmarshall_error "Row does not have ref atrribute")
in
let ctime =
match ctime_l with
| [(_, ctime_s)] ->
Expand Down