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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6735) A minor optimization to avoid pread() be blocked by read() inside the same DFSInputStream
Date Wed, 26 Nov 2014 22:21:13 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6735?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14226896#comment-14226896

stack commented on HDFS-6735:

Interesting CachingStrategy can be changed on a DFSIS post-construction. Could avoid infolock
on cachingstrategy if pre-made the readahead and dropbehinds but that's probably OTT.

Nice doc'ing of locking strategy around data members.

If we are doing a openInfo call, we can't service a filelength; I suppose thats how it should
be; if we are updating our block info, file length could change.... and if updating block
info, somethings up w/ the block set we currently have...  At least the lock has climbed down
from a lock on 'this'.  Good.

Patch LGTM (I like the Colin feedback above).  Numbers still pretty good [~larsh]?

> 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-v3.txt, HDFS-6735-v4.txt, HDFS-6735-v5.txt,
HDFS-6735-v6.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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