Measure changed-key work on large collections

test/test_incremental.ml

@@ -856,3 +856,42 @@ let differential_cases =
     ( "the incremental plan matches full evaluation on a short run",
       fun () -> differential_case 5 20 );
   ]
+
+let regression_cases =
+  [
+    ( "a single key update on a large collection touches only that key",
+      fun () ->
+        let entries =
+          Util.list_init 500 (fun index -> (index + 1, order_row (Printf.sprintf "customer%d" index) ((index * 37) mod 4001)))
+        in
+        let fixture = build_fixture (read_fixture "expensive_order.delta") entries in
+        Delta_runtime.reset_counters fixture.fx_counters;
+        (match step fixture [ Change.OpReplace (250, order_row "customer250" 3000) ] with
+        | Error message -> fail "update" message
+        | Ok (applied, cached, _) ->
+            let counters = fixture.fx_counters in
+            check_equal_int "predicate evaluations" 1 counters.Delta_runtime.predicate_evaluations;
+            check_equal_int "mapping evaluations" 0 counters.Delta_runtime.mapping_evaluations;
+            check_equal_int "scalar deltas" 1 counters.Delta_runtime.scalar_deltas;
+            check_equal_int "changed key visits" 3 counters.Delta_runtime.changed_key_visits;
+            check_equal_int "full traversals" 0 counters.Delta_runtime.full_traversals;
+            check_equal_string "result matches the reference"
+              (Value.to_string (reference_result fixture fixture.fx_state))
+              (Value.to_string applied);
+            check_equal_string "cache matches the reference"
+              (Value.to_string (reference_result fixture fixture.fx_state))
+              (Value.to_string cached)) );
+    ( "an inserted key only evaluates the predicate and mapping for itself",
+      fun () ->
+        let entries = Util.list_init 500 (fun index -> (index + 1, order_row "row" 10)) in
+        let fixture = build_fixture (read_fixture "expensive_order.delta") entries in
+        Delta_runtime.reset_counters fixture.fx_counters;
+        (match step fixture [ Change.OpInsert (501, order_row "newcomer" 5000) ] with
+        | Error message -> fail "insert" message
+        | Ok _ ->
+            let counters = fixture.fx_counters in
+            check_equal_int "predicate evaluations" 1 counters.Delta_runtime.predicate_evaluations;
+            check_equal_int "mapping evaluations" 1 counters.Delta_runtime.mapping_evaluations;
+            check_equal_int "changed key visits" 3 counters.Delta_runtime.changed_key_visits;
+            check_equal_int "full traversals" 0 counters.Delta_runtime.full_traversals) );
+  ]