Make shard balancing deterministic if weights are identical #4866
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| @@ -804,7 +804,8 @@ private boolean tryRelocateShard(Operation operation, ModelNode minNode, ModelNo | |||
| if ((srcDecision = maxNode.removeShard(shard)) != null) { | |||
| minNode.addShard(shard, srcDecision); | |||
| final float delta = weight.weight(operation, this, minNode, idx) - weight.weight(operation, this, maxNode, idx); | |||
| if (delta < minCost) { | |||
| if (delta < minCost || | |||
| (candidate != null && delta == minCost && candidate.id() > shard.id())) { | |||
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Looks good. Maybe there could just be a comment that this tie-breaker is necessary to make shard balancing deterministic?
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I already added it :) updateing in a sec and referencing the corresponding issue.
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+1 |
It happens to be the case that the iteration order of a HashMaps keyset might be different across runs. This can cause undeterministic results in shard balancing if weights are identical and multiple shards of the same index are eligable for relocation. This commit adds a tie-breaker based on the shard ID to prioritise the lowest shard ID. This also makes `AddIncrementallyTests#testAddNodesAndIndices` reproducible. Closes elastic#4867
lcawl
added
:Distributed/Distributed
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It happens to be the case that the iteration order of a HashMaps
keyset might be different across runs. This can cause undeterministic
results in shard balancing if weights are identical and multiple shards
of the same index are eligable for relocation. This commit adds
a tie-breaker based on the shard ID to prioritise the lowest shard
ID. This also makes
AddIncrementallyTests#testAddNodesAndIndicesreproducible.