Allow targets to exceed floor, add another check
Sometimes we want to transfer a shard to a target even though it's
already at the floor. We add another check to make sure we're not
wasitng effort -- the difference in shard counts between the source and
the target must be 2 or greater.
We also refactor the global shard count code to avoid future atom /
binary problems.
BugzID: 24466
diff --git a/src/mem3_rebalance.erl b/src/mem3_rebalance.erl
index b7d161c..5589e45 100644
--- a/src/mem3_rebalance.erl
+++ b/src/mem3_rebalance.erl
@@ -135,7 +135,7 @@
lists:member(Node, TargetNodes)
end, shard_count_by_node(LocalOps)),
TotalCount = lists:foldl(fun({_, C}, Sum) -> Sum + C end, 0, CountByNode),
- TargetLevel = (TotalCount div length(TargetNodes)) + 1,
+ TargetLevel = TotalCount div length(TargetNodes),
FoldFun = fun
(_, Acc) when length(Acc) >= Limit ->
% We've already accumulated the max number of shard ops.
@@ -176,11 +176,12 @@
InZone = filter_map_by_zone(shards_by_node(Shards, Nodes), Zone),
SortedByCount = lists:sort(smallest_first(Moves), InZone),
SourceCount = get_shard_count(Node, SortedByCount),
+ GlobalShardCounts = shard_count_by_node(Moves),
+ TotalSource = get_global_shard_count(Node, GlobalShardCounts),
Fun = fun({CandidateNode, OwnShards}) ->
HasRange = lists:keymember(Shard#shard.range, #shard.range, OwnShards),
TargetCount = get_shard_count(CandidateNode, SortedByCount),
- NodeKey = couch_util:to_binary(CandidateNode),
- Total = couch_util:get_value(NodeKey, shard_count_by_node(Moves)),
+ TotalTarget = get_global_shard_count(CandidateNode, GlobalShardCounts),
if
CandidateNode =:= Node ->
% Can't move a shard to ourselves
@@ -191,8 +192,11 @@
TargetCount >= SourceCount ->
% Executing this move would create a local imbalance in the DB
true;
- Total >= TargetLevel ->
- % The candidate has already achieved the target level
+ TotalTarget > TargetLevel ->
+ % The candidate has already exceeded the target level
+ true;
+ (TotalSource - TotalTarget) < 2 ->
+ % Donating here is wasted work
true;
true ->
false
@@ -216,6 +220,11 @@
get_shard_count(AtomKey, ShardsByNode) when is_atom(AtomKey) ->
length(couch_util:get_value(AtomKey, ShardsByNode, [])).
+get_global_shard_count(Node, Counts) when is_atom(Node) ->
+ get_global_shard_count(couch_util:to_binary(Node), Counts);
+get_global_shard_count(Node, Counts) when is_binary(Node) ->
+ couch_util:get_value(Node, Counts, 0).
+
compute_moves(IdealZoning, IdealZoning, _Copies, OtherMoves) ->
OtherMoves;
compute_moves(IdealZoning, ActualZoning, Copies, OtherMoves) ->
@@ -330,8 +339,8 @@
fun(A, B) -> sort_by_count(A, B, Global) =< 0 end.
sort_by_count({NodeA, SA}, {NodeB, SB}, Global) when length(SA) =:= length(SB) ->
- CountA = couch_util:get_value(couch_util:to_binary(NodeA), Global, 0),
- CountB = couch_util:get_value(couch_util:to_binary(NodeB), Global, 0),
+ CountA = get_global_shard_count(NodeA, Global),
+ CountB = get_global_shard_count(NodeB, Global),
cmp(CountA, CountB);
sort_by_count({_, A}, {_, B}, _) ->
cmp(length(A), length(B)).
