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From rnew...@apache.org
Subject [33/50] mem3 commit: updated refs/heads/master to 64c0c74
Date Thu, 28 Aug 2014 12:22:53 GMT
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


Project: http://git-wip-us.apache.org/repos/asf/couchdb-mem3/repo
Commit: http://git-wip-us.apache.org/repos/asf/couchdb-mem3/commit/a6ca5c6f
Tree: http://git-wip-us.apache.org/repos/asf/couchdb-mem3/tree/a6ca5c6f
Diff: http://git-wip-us.apache.org/repos/asf/couchdb-mem3/diff/a6ca5c6f

Branch: refs/heads/master
Commit: a6ca5c6fa36f8b49bf7785a932b30aef8693b286
Parents: 5c3c9c9
Author: Adam Kocoloski <adam@cloudant.com>
Authored: Wed Oct 30 14:17:03 2013 -0400
Committer: Robert Newson <rnewson@apache.org>
Committed: Wed Jul 23 18:46:27 2014 +0100

----------------------------------------------------------------------
 src/mem3_rebalance.erl | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/couchdb-mem3/blob/a6ca5c6f/src/mem3_rebalance.erl
----------------------------------------------------------------------
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 @@ global_expand(TargetNodes0, LocalOps, Limit) ->
         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 @@ donate_fold(#shard{node = Node} = Shard, #gacc{node = Node} = Acc0)
->
     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 @@ donate_fold(#shard{node = Node} = Shard, #gacc{node = Node} = Acc0) ->
             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 @@ donate_fold(_Shard, Acc) ->
 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 @@ smallest_first(PrevMoves) ->
     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)).


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