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From zzh...@apache.org
Subject git commit: HELIX-148: Current preferred placement for auto rebalace is suboptimal for n > p
Date Mon, 29 Jul 2013 23:18:54 GMT
Updated Branches:
  refs/heads/master 04ca91bd8 -> 937bc9aa0


HELIX-148: Current preferred placement for auto rebalace is suboptimal for n > p


Project: http://git-wip-us.apache.org/repos/asf/incubator-helix/repo
Commit: http://git-wip-us.apache.org/repos/asf/incubator-helix/commit/937bc9aa
Tree: http://git-wip-us.apache.org/repos/asf/incubator-helix/tree/937bc9aa
Diff: http://git-wip-us.apache.org/repos/asf/incubator-helix/diff/937bc9aa

Branch: refs/heads/master
Commit: 937bc9aa06cccb7b021972b0a904f7d6dc791d78
Parents: 04ca91b
Author: zzhang <zzhang5@uci.edu>
Authored: Mon Jul 29 16:18:47 2013 -0700
Committer: zzhang <zzhang5@uci.edu>
Committed: Mon Jul 29 16:18:47 2013 -0700

----------------------------------------------------------------------
 .../controller/strategy/AutoRebalanceStrategy.java    | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/incubator-helix/blob/937bc9aa/helix-core/src/main/java/org/apache/helix/controller/strategy/AutoRebalanceStrategy.java
----------------------------------------------------------------------
diff --git a/helix-core/src/main/java/org/apache/helix/controller/strategy/AutoRebalanceStrategy.java
b/helix-core/src/main/java/org/apache/helix/controller/strategy/AutoRebalanceStrategy.java
index ee398d2..58f5f17 100644
--- a/helix-core/src/main/java/org/apache/helix/controller/strategy/AutoRebalanceStrategy.java
+++ b/helix-core/src/main/java/org/apache/helix/controller/strategy/AutoRebalanceStrategy.java
@@ -420,13 +420,23 @@ public class AutoRebalanceStrategy implements Rebalancer {
       Map<Replica, Node> preferredMapping;
       preferredMapping = new HashMap<Replica, Node>();
       int partitionId = 0;
-
       for (String partition : _partitions) {
         int replicaId = 0;
         for (String state : _states.keySet()) {
           for (int i = 0; i < _states.get(state); i++) {
             Replica replica = new Replica(partition, state, i);
-            int index = (partitionId + replicaId) % allNodes.size();
+            int index;
+            if (allNodes.size() > _partitions.size()) {
+              // assign replicas in partition order in case there are more nodes than partitions
+              index = (partitionId + replicaId * _partitions.size()) % allNodes.size();
+            } else if (allNodes.size() == _partitions.size()) {
+              // need a replica offset in case the sizes of these sets are the same
+              index = ((partitionId + replicaId * _partitions.size()) % allNodes.size()
+                  + replicaId) % allNodes.size();
+            } else {
+              // in all other cases, assigning a replica at a time for each partition is
reasonable
+              index = (partitionId + replicaId) % allNodes.size();
+            }
             preferredMapping.put(replica, _nodeMap.get(allNodes.get(index)));
             replicaId = replicaId + 1;
           }


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