Merge branch 'dgud/mnesia/index-timing/OTP-12972' into maint

* dgud/mnesia/index-timing/OTP-12972:
  mnesia: Improve index updates

2 files changed, 35 insertions, 11 deletions

diff --git a/lib/mnesia/src/mnesia_index.erl b/lib/mnesia/src/mnesia_index.erl
index 81ed5a8f1a..0c882c0df6 100644
--- a/lib/mnesia/src/mnesia_index.erl
+++ b/lib/mnesia/src/mnesia_index.erl
@@ -70,17 +70,24 @@ add_index(Index, Tab, Key, Obj, Old) ->
 add_index2([{Pos, Ixt} |Tail], bag, Tab, K, Obj, OldRecs) ->
     db_put(Ixt, {element(Pos, Obj), K}),
     add_index2(Tail, bag, Tab, K, Obj, OldRecs);
-add_index2([{Pos, Ixt} |Tail], Type, Tab, K, Obj, OldRecs) ->
+add_index2([{Pos, Ixt} |Tail], Type, Tab, K, Obj, OldRecs0) ->
     %% Remove old tuples in index if Tab is updated
-    case OldRecs of 
-	undefined -> 
-	    Old = mnesia_lib:db_get(Tab, K),
-	    del_ixes(Ixt, Old, Pos, K);
-	Old -> 
-	    del_ixes(Ixt, Old, Pos, K)
-    end,
-    db_put(Ixt, {element(Pos, Obj), K}),
-    add_index2(Tail, Type, Tab, K, Obj, OldRecs);
+    OldRecs1 = case OldRecs0 of
+		   undefined -> mnesia_lib:db_get(Tab, K);
+		   _ -> OldRecs0
+	       end,
+    IdxVal = element(Pos, Obj),
+    case [Old || Old <- OldRecs1, element(Pos, Old) =/= IdxVal] of
+	[] when OldRecs1 =:= [] ->  %% Write
+	    db_put(Ixt, {element(Pos, Obj), K}),
+	    add_index2(Tail, Type, Tab, K, Obj, OldRecs0);
+	[] -> %% when OldRecs1 =/= [] Update without modifying index field
+	    add_index2(Tail, Type, Tab, K, Obj, OldRecs0);
+	OldRecs -> %% Update
+	    db_put(Ixt, {element(Pos, Obj), K}),
+	    del_ixes(Ixt, OldRecs, Pos, K),
+	    add_index2(Tail, Type, Tab, K, Obj, OldRecs0)
+    end;
 add_index2([], _, _Tab, _K, _Obj, _) -> ok.
 
 delete_index(Index, Tab, K) ->
diff --git a/lib/mnesia/test/mnesia_dirty_access_test.erl b/lib/mnesia/test/mnesia_dirty_access_test.erl
index 89aff2b3b8..0d57e5a1b1 100644
--- a/lib/mnesia/test/mnesia_dirty_access_test.erl
+++ b/lib/mnesia/test/mnesia_dirty_access_test.erl
@@ -401,9 +401,26 @@ dirty_index_read(Config, Storage) ->
     ?match({'EXIT', _},  mnesia:dirty_index_read(Tab, 2, BadValPos)), 
     ?match({'EXIT', _},  mnesia:dirty_index_read(foo, 2, ValPos)), 
     ?match({'EXIT', _},  mnesia:dirty_index_read([], 2, ValPos)), 
-    
+
+    mnesia:dirty_write({Tab, 5, 1}),
+    ?match(ok, index_read_loop(Tab, 0)),
+
     ?verify_mnesia(Nodes, []).
 
+
+index_read_loop(Tab, N) when N =< 1000 ->
+    spawn_link(fun() ->
+		       mnesia:transaction(fun() -> mnesia:write({Tab, 5, 1}) end)
+	       end),
+    case mnesia:dirty_match_object({Tab, '_', 1}) of
+	[{Tab, 5, 1}] ->
+	    index_read_loop(Tab, N+1);
+	Other -> {N, Other}
+    end;
+index_read_loop(_, _) ->
+    ok.
+
+
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