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https://issues.apache.org/jira/browse/CASSANDRA-12884?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16119980#comment-16119980
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Daniel Cranford commented on CASSANDRA-12884:
---------------------------------------------

Same bug. Regression.

> Batch logic can lead to unbalanced use of system.batches
> --------------------------------------------------------
>
>                 Key: CASSANDRA-12884
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12884
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Adam Hattrell
>            Assignee: Joshua McKenzie
>             Fix For: 3.0.x, 3.11.x
>
>         Attachments: 0001-CASSANDRA-12884.patch
>
>
> It looks as though there are some odd edge cases in how we distribute the 
> copies in system.batches.
> The main issue is in the filter method for 
> org.apache.cassandra.batchlog.BatchlogManager
> {code:java}
>  if (validated.size() - validated.get(localRack).size() >= 2)
>  {
>         // we have enough endpoints in other racks
>         validated.removeAll(localRack);
>   }
>  if (validated.keySet().size() == 1)
>  {
>        // we have only 1 `other` rack
>        Collection otherRack = 
> Iterables.getOnlyElement(validated.asMap().values());
>        
>         return Lists.newArrayList(Iterables.limit(otherRack, 2));
>  }
> {code}
> So with one or two racks we just return the first 2 entries in the list.  
> There's no shuffle or randomisation here.



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