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https://issues.apache.org/jira/browse/HDFS-15255?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17076380#comment-17076380
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Stephen O'Donnell commented on HDFS-15255:
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{quote}
If both are set, then the comparator here would return both.
Since in follow code, when call Collections.sort(list, comp), list has been
sorted.
{quote}
I'm not sure if that is correct. This method does not actually do the sorting.
Rather it returns a `Consumer<>` object which seems to contain a comparator.
This is then passed to `networktopology.sortByDistance` where the actual sort
is applied.
Reading this method, I think it returns only one "sort". It starts as a
shuffle. If `readConsiderLoad` is set, it overwrites it. If
`readConsiderStorageType` is also set, it overwrites it again and the last one
set wins and is returned. I don't think each sort is applied on top of the last.
In saying the above, this syntax is a bit unfamiliar to me, so I may be wrong!
> Consider StorageType when DatanodeManager#sortLocatedBlock()
> ------------------------------------------------------------
>
> Key: HDFS-15255
> URL: https://issues.apache.org/jira/browse/HDFS-15255
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Lisheng Sun
> Assignee: Lisheng Sun
> Priority: Major
> Attachments: HDFS-15255.001.patch, HDFS-15255.002.patch
>
>
> When only one replica of a block is SDD, the others are HDD.
> When the client reads the data, the current logic is that it considers the
> distance between the client and the dn. I think it should also consider the
> StorageType of the replica. Priority to return a replica of the specified
> StorageType
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