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https://issues.apache.org/jira/browse/IGNITE-3195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16917614#comment-16917614
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Anton Vinogradov commented on IGNITE-3195:
------------------------------------------

Discussed privately with [~ascherbakov].

1) Historical rebalance semantic was not changed due to data foss found at 
TeamCity regression.
Issue IGNITE-12117 created to un-stripe it.

2) Reordering is not possible during messages registration since ordered topic 
used, so no problem here.

3) It is possible to have X2 load in the following cases:
3.1 node supplies and demands simultaneously
3.2 node demands in a historical and regular way simultaneously
that seems to be not a production case 
3.1 can be solved by baseline and good affinity
3.2 almost impossible at a real environment to have some partition rebalanced 
using historical rebalance when others should be rebalanced using a regular one.

> Rebalancing: IgniteConfiguration.rebalanceThreadPoolSize is wrongly treated
> ---------------------------------------------------------------------------
>
>                 Key: IGNITE-3195
>                 URL: https://issues.apache.org/jira/browse/IGNITE-3195
>             Project: Ignite
>          Issue Type: Bug
>          Components: cache
>            Reporter: Denis Magda
>            Assignee: Anton Vinogradov
>            Priority: Major
>              Labels: iep-16
>             Fix For: 2.8
>
>          Time Spent: 3h 50m
>  Remaining Estimate: 0h
>
> Presently it's considered that the maximum number of threads that has to 
> process all demand and supply messages coming from all the nodes must not be 
> bigger than {{IgniteConfiguration.rebalanceThreadPoolSize}}.
> Current implementation relies on ordered messages functionality creating a 
> number of topics equal to {{IgniteConfiguration.rebalanceThreadPoolSize}}.
> However, the implementation doesn't take into account that ordered messages, 
> that correspond to a particular topic, are processed in parallel for 
> different nodes. Refer to the implementation of 
> {{GridIoManager.processOrderedMessage}} to see that for every topic there 
> will be a unique {{GridCommunicationMessageSet}} for every node.
> Also to prove that this is true you can refer to this execution stack 
> {noformat}
> java.lang.RuntimeException: HAPPENED DEMAND
>       at 
> org.apache.ignite.internal.processors.cache.GridCachePartitionExchangeManager$5.apply(GridCachePartitionExchangeManager.java:378)
>       at 
> org.apache.ignite.internal.processors.cache.GridCachePartitionExchangeManager$5.apply(GridCachePartitionExchangeManager.java:364)
>       at 
> org.apache.ignite.internal.processors.cache.GridCacheIoManager.processMessage(GridCacheIoManager.java:622)
>       at 
> org.apache.ignite.internal.processors.cache.GridCacheIoManager.onMessage0(GridCacheIoManager.java:320)
>       at 
> org.apache.ignite.internal.processors.cache.GridCacheIoManager.access$300(GridCacheIoManager.java:81)
>       at 
> org.apache.ignite.internal.processors.cache.GridCacheIoManager$OrderedMessageListener.onMessage(GridCacheIoManager.java:1125)
>       at 
> org.apache.ignite.internal.managers.communication.GridIoManager.invokeListener(GridIoManager.java:1219)
>       at 
> org.apache.ignite.internal.managers.communication.GridIoManager.access$1600(GridIoManager.java:105)
>       at 
> org.apache.ignite.internal.managers.communication.GridIoManager$GridCommunicationMessageSet.unwind(GridIoManager.java:2456)
>       at 
> org.apache.ignite.internal.managers.communication.GridIoManager.unwindMessageSet(GridIoManager.java:1179)
>       at 
> org.apache.ignite.internal.managers.communication.GridIoManager.access$1900(GridIoManager.java:105)
>       at 
> org.apache.ignite.internal.managers.communication.GridIoManager$6.run(GridIoManager.java:1148)
>       at 
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
>       at 
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
>       at java.lang.Thread.run(Thread.java:745)
> {noformat}
> All this means that in fact the number of threads that will be busy with 
> replication activity will be equal to 
> {{IgniteConfiguration.rebalanceThreadPoolSize}} x 
> number_of_nodes_participated_in_rebalancing



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