Merge branch 'uw/mnesia-majority' into dev

* uw/mnesia-majority:
  dialyzer warning on mnesia_tm
  Add documentation text about majority checking
  add mnesia_majority_test suite
  where_to_wlock optimization + change_table_majority/2
  bug in mnesia_tm:needs_majority/2
  optimize sticky_lock maj. check
  check majority for sticky locks
  Write locks now check majority when needed.
  Add {majority, boolean()} per-table option.

OTP-9304

1 files changed, 58 insertions, 11 deletions

diff --git a/lib/mnesia/src/mnesia_locker.erl b/lib/mnesia/src/mnesia_locker.erl
index ca0cc79c45..0492d794f3 100644
--- a/lib/mnesia/src/mnesia_locker.erl
+++ b/lib/mnesia/src/mnesia_locker.erl
@@ -40,7 +40,8 @@
 	 sticky_wlock_table/3,
 	 wlock/3,
 	 wlock_no_exist/4,
-	 wlock_table/3
+	 wlock_table/3,
+	 load_lock_table/3
 	]).
 
 %% sys callback functions
@@ -656,16 +657,17 @@ rwlock(Tid, Store, Oid) ->
 	    Lock = write,
 	    case need_lock(Store, Tab, Key, Lock)  of
 		yes ->
-		    Ns = w_nodes(Tab),
+		    {Ns, Majority} = w_nodes(Tab),
+		    check_majority(Majority, Tab, Ns),
 		    Res = get_rwlocks_on_nodes(Ns, rwlock, Node, Store, Tid, Oid),
 		    ?ets_insert(Store, {{locks, Tab, Key}, Lock}),
 		    Res;
 		no ->
 		    if
 			Key == ?ALL ->
-			    w_nodes(Tab);
+			    element(2, w_nodes(Tab));
 			Tab == ?GLOBAL ->
-			    w_nodes(Tab);
+			    element(2, w_nodes(Tab));
 			true ->
 			    dirty_rpc(Node, Tab, Key, Lock)
 		    end
@@ -677,12 +679,34 @@ rwlock(Tid, Store, Oid) ->
 %% in the local store under the key == nodes
 
 w_nodes(Tab) ->
-    Nodes = ?catch_val({Tab, where_to_write}),
-    case Nodes of
-	[_ | _] -> Nodes;
+    case ?catch_val({Tab, where_to_wlock}) of
+	{[_ | _], _} = Where -> Where;
 	_ ->  mnesia:abort({no_exists, Tab})
     end.
 
+%% If the table has the 'majority' flag set, we can
+%% only take a write lock if we see a majority of the
+%% nodes.
+
+
+check_majority(true, Tab, HaveNs) ->
+    check_majority(Tab, HaveNs);
+check_majority(false, _, _) ->
+    ok.
+
+check_majority(Tab, HaveNs) ->
+    case ?catch_val({Tab, majority}) of
+	true ->
+	    case mnesia_lib:have_majority(Tab, HaveNs) of
+		true ->
+		    ok;
+		false ->
+		    mnesia:abort({no_majority, Tab})
+	    end;
+	_ ->
+	    ok
+    end.
+
 %% aquire a sticky wlock, a sticky lock is a lock
 %% which remains at this node after the termination of the
 %% transaction.
@@ -708,12 +732,14 @@ sticky_lock(Tid, Store, {Tab, Key} = Oid, Lock) ->
     end.
 
 do_sticky_lock(Tid, Store, {Tab, Key} = Oid, Lock) ->
+    {WNodes, Majority} = w_nodes(Tab),
+    sticky_check_majority(Lock, Tab, Majority, WNodes),
     ?MODULE ! {self(), {test_set_sticky, Tid, Oid, Lock}},
     N = node(),
     receive
 	{?MODULE, N, granted} ->
 	    ?ets_insert(Store, {{locks, Tab, Key}, write}),
-	    [?ets_insert(Store, {nodes, Node}) || Node <- w_nodes(Tab)],
+	    [?ets_insert(Store, {nodes, Node}) || Node <- WNodes],
 	    granted;
 	{?MODULE, N, {granted, Val}} -> %% for rwlocks
 	    case opt_lookup_in_client(Val, Oid, write) of
@@ -721,7 +747,7 @@ do_sticky_lock(Tid, Store, {Tab, Key} = Oid, Lock) ->
 		    exit({aborted, C});
 		Val2 ->
 		    ?ets_insert(Store, {{locks, Tab, Key}, write}),
-		    [?ets_insert(Store, {nodes, Node}) || Node <- w_nodes(Tab)],
+		    [?ets_insert(Store, {nodes, Node}) || Node <- WNodes],
 		    Val2
 	    end;
 	{?MODULE, N, {not_granted, Reason}} ->
@@ -737,6 +763,16 @@ do_sticky_lock(Tid, Store, {Tab, Key} = Oid, Lock) ->
 	    dirty_sticky_lock(Tab, Key, [N], Lock)
     end.
 
+sticky_check_majority(W, Tab, true, WNodes) when W==write; W==read_write ->
+    case mnesia_lib:have_majority(Tab, WNodes) of
+	true ->
+	    ok;
+	false ->
+	    mnesia:abort({no_majority, Tab})
+    end;
+sticky_check_majority(_, _, _, _) ->
+    ok.
+
 not_stuck(Tid, Store, Tab, _Key, Oid, _Lock, N) ->
     rlock(Tid, Store, {Tab, ?ALL}),   %% needed?
     wlock(Tid, Store, Oid),           %% perfect sync
@@ -773,22 +809,33 @@ sticky_wlock_table(Tid, Store, Tab) ->
 %% local store when we have aquired the lock.
 %% 
 wlock(Tid, Store, Oid) ->
+    wlock(Tid, Store, Oid, _CheckMajority = true).
+
+wlock(Tid, Store, Oid, CheckMajority) ->
     {Tab, Key} = Oid,
     case need_lock(Store, Tab, Key, write) of
 	yes ->
-	    Ns = w_nodes(Tab),
+	    {Ns, Majority} = w_nodes(Tab),
+	    if CheckMajority ->
+		    check_majority(Majority, Tab, Ns);
+	       true ->
+		    ignore
+	    end,
 	    Op = {self(), {write, Tid, Oid}},
 	    ?ets_insert(Store, {{locks, Tab, Key}, write}),
 	    get_wlocks_on_nodes(Ns, Ns, Store, Op, Oid);
 	no when Key /= ?ALL, Tab /= ?GLOBAL ->
 	    [];
 	no ->
-	    w_nodes(Tab)
+	    element(2, w_nodes(Tab))
     end.
 
 wlock_table(Tid, Store, Tab) ->
     wlock(Tid, Store, {Tab, ?ALL}).
 
+load_lock_table(Tid, Store, Tab) ->
+    wlock(Tid, Store, {Tab, ?ALL}, _CheckMajority = false).
+
 %% Write lock even if the table does not exist
 
 wlock_no_exist(Tid, Store, Tab, Ns) ->