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https://issues.apache.org/jira/browse/HDFS-6735?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14193629#comment-14193629
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Lars Hofhansl commented on HDFS-6735:
-------------------------------------
As described in HDFS-6698, the potential performance gains for something like
HBase are substantial.
I agree it's better to keep LocatedBlocks as not threadsafe and require called
to lock accordingly.
I've not see fetchAt in a hot path (at least not from HBase usage patterns).
seek + read (non positional) cannot be done concurrently, agreed. pread should
be possible, though.
How should we continue to move on this? Seems important. :)
Also open to suggestions about how to fix things in HBase (see last comment in
HDFS-6698, about how HBase handles things and how limited concurrency "within"
an InputStream is an issue).
> A minor optimization to avoid pread() be blocked by read() inside the same
> DFSInputStream
> -----------------------------------------------------------------------------------------
>
> Key: HDFS-6735
> URL: https://issues.apache.org/jira/browse/HDFS-6735
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client
> Affects Versions: 3.0.0
> Reporter: Liang Xie
> Assignee: Liang Xie
> Attachments: HDFS-6735-v2.txt, HDFS-6735.txt
>
>
> In current DFSInputStream impl, there're a couple of coarser-grained locks in
> read/pread path, and it has became a HBase read latency pain point so far. In
> HDFS-6698, i made a minor patch against the first encourtered lock, around
> getFileLength, in deed, after reading code and testing, it shows still other
> locks we could improve.
> In this jira, i'll make a patch against other locks, and a simple test case
> to show the issue and the improved result.
> This is important for HBase application, since in current HFile read path, we
> issue all read()/pread() requests in the same DFSInputStream for one HFile.
> (Multi streams solution is another story i had a plan to do, but probably
> will take more time than i expected)
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