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https://issues.apache.org/jira/browse/HDFS-6735?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14071335#comment-14071335
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Liang Xie commented on HDFS-6735:
---------------------------------
This patch includes HDFS-6698 already.
With the source change, the added "testPreadBlockedbyRead" result in my box:
{code}
grep cost
hadoop-hdfs-project/hadoop-hdfs/target/surefire-reports/org.apache.hadoop.hdfs.TestPread-output.txt
read() cost:5008ms, pread() cost:5ms
{code}
Without the source change(off cause, you still need keep the "readDelay"
injecting faults in src code), the added "testPreadBlockedbyRead" result in my
box:
{code}
read() cost:5009ms, pread() cost:4912ms
{code}
> 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.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.
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