[jira] [Updated] (KAFKA-1183) DefaultEventHandler causes unbalanced distribution of messages across partitions

["Jason Gustafson (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-1183?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jason Gustafson updated KAFKA-1183:
-----------------------------------
    Fix Version/s:     (was: 0.10.1.0)
                       (was: 0.8.1)

> DefaultEventHandler causes unbalanced distribution of messages across partitions
> --------------------------------------------------------------------------------
>
>                 Key: KAFKA-1183
>                 URL: https://issues.apache.org/jira/browse/KAFKA-1183
>             Project: Kafka
>          Issue Type: Bug
>          Components: producer 
>    Affects Versions: 0.8.0
>            Reporter: Dragos Dena
>            Assignee: Jun Rao
>         Attachments: KAFKA-1183-trunk.patch
>
>
> KAFKA-959 introduced an optimisation in {{DefaultEventHandler}} that was supposed to have the effect of sending all messages from the same batch to a single partition if no key is specified.
> The problem is that the {{sendPartitionPerTopicCache}} cache, which holds the current selected partition for each topic, isn't actually invalided at the start or end of each batch.
> The observed result is that, after the first request chooses a random partition, all subsequent messages from that producer land in the same partition. If you have a large number of producers, then it should be fine, but if your producer count is comparable to the partition count, then it will get unbalanced.



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