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https://issues.apache.org/jira/browse/KAFKA-188?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13486220#comment-13486220
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Jay Kreps commented on KAFKA-188:
---------------------------------
Okay, you and Neha are giving conflicting advice on ReplicaManager. Can I omit
the case where there is no replica? That is what is complicating this method,
because if there is no replica then will there be a log to get the parent
directory from?
If so then I am left with:
def checkpointHighWatermarks() {
val replicas =
allPartitions.values.map(_.getReplica(config.brokerId)).collect{case
Some(replica) => replica}
val replicasByDir =
replicas.filter(_.log.isDefined).groupBy(_.log.get.dir.getParent)
for((dir, reps) <- replicasByDir) {
val hwms = reps.map(r => (TopicAndPartition(r.topic, r.partitionId) ->
r.highWatermark)).toMap
highWatermarkCheckpoints(dir).write(hwms)
}
}
which is much simpler. lmk.
> Support multiple data directories
> ---------------------------------
>
> Key: KAFKA-188
> URL: https://issues.apache.org/jira/browse/KAFKA-188
> Project: Kafka
> Issue Type: New Feature
> Reporter: Jay Kreps
> Attachments: KAFKA-188.patch, KAFKA-188-v2.patch, KAFKA-188-v3.patch,
> KAFKA-188-v4.patch, KAFKA-188-v5.patch
>
>
> Currently we allow only a single data directory. This means that a multi-disk
> configuration needs to be a RAID array or LVM volume or something like that
> to be mounted as a single directory.
> For a high-throughput low-reliability configuration this would mean RAID0
> striping. Common wisdom in Hadoop land has it that a JBOD setup that just
> mounts each disk as a separate directory and does application-level balancing
> over these results in about 30% write-improvement. For example see this claim
> here:
> http://old.nabble.com/Re%3A-RAID-vs.-JBOD-p21466110.html
> It is not clear to me why this would be the case--it seems the RAID
> controller should be able to balance writes as well as the application so it
> may depend on the details of the setup.
> Nonetheless this would be really easy to implement, all you need to do is add
> multiple data directories and balance partition creation over these disks.
> One problem this might cause is if a particular topic is much larger than the
> others it might unbalance the load across the disks. The partition->disk
> assignment policy should probably attempt to evenly spread each topic to
> avoid this, rather than just trying keep the number of partitions balanced
> between disks.
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