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https://issues.apache.org/jira/browse/KAFKA-691?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13549842#comment-13549842
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Jun Rao commented on KAFKA-691:
-------------------------------
Thanks for the patch. Overall, the patch is pretty good and is well thought
out. Some comments:
1. DefaultEventHandler:
1.1 In handle(), I don't think we need to add the if test in the following
statement. The reason is that a message could fail to be sent because the
leader changes immediately after the previous metadata refresh. Normally,
leaders are elected very quickly. So, it makes sense to refresh the metadata
again.
if (topicMetadataToRefresh.nonEmpty)
Utils.swallowError(brokerPartitionInfo.updateInfo(outstandingProduceRequests.map(_.topic).toSet))
1.2 In handle(), it seems that it's better to call the following code before
dispatchSerializedData().
if (topicMetadataRefreshInterval >= 0 &&
SystemTime.milliseconds - lastTopicMetadataRefresh >
topicMetadataRefreshInterval) {
Utils.swallowError(brokerPartitionInfo.updateInfo(topicMetadataToRefresh.toSet))
topicMetadataToRefresh.clear
lastTopicMetadataRefresh = SystemTime.milliseconds
}
1.3 getPartition(): If none of the partitions is available, we should throw
LeaderNotAvailableException, instead of UnknownTopicOrPartitionException.
2. DefaultPartitioner: Since key is not expected to be null, we should remove
the code that deals with null key.
3. The consumer side logic is fine. The consumer rebalance is only triggered
when there are changes in partitions, not when there are changes in the
availability of the partition. The rebalance logic doesn't depend on a
partition being available. If a partition is not available,
ConsumerFetcherManager will keep refreshing metadata. If you have a replication
factor of 1, you will need to set a larger refresh.leader.backoff.ms, if a
broker is expected to go down for a long time.
> Fault tolerance broken with replication factor 1
> ------------------------------------------------
>
> Key: KAFKA-691
> URL: https://issues.apache.org/jira/browse/KAFKA-691
> Project: Kafka
> Issue Type: Bug
> Affects Versions: 0.8
> Reporter: Jay Kreps
> Attachments: KAFKA-691-v1.patch
>
>
> In 0.7 if a partition was down we would just send the message elsewhere. This
> meant that the partitioning was really more of a "stickiness" then a hard
> guarantee. This made it impossible to depend on it for partitioned, stateful
> processing.
> In 0.8 when running with replication this should not be a problem generally
> as the partitions are now highly available and fail over to other replicas.
> However in the case of replication factor = 1 no longer really works for most
> cases as now a dead broker will give errors for that broker.
> I am not sure of the best fix. Intuitively I think this is something that
> should be handled by the Partitioner interface. However currently the
> partitioner has no knowledge of which nodes are available. So you could use a
> random partitioner, but that would keep going back to the down node.
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