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https://issues.apache.org/jira/browse/HDFS-941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13050231#comment-13050231
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Todd Lipcon commented on HDFS-941:
----------------------------------
Ran the following benchmark to compare 0.22 before vs after the application of
HDFS-941:
- inserted a 128M file into HDFS
- read it 50 times using "hadoop fs -cat /file > /dev/null" and the unix "time"
utility
- recompiled with the patch reverted, restarted NN/DN
- ran same test
- recompiled with the patch included, restarted NN/DN
- ran same test
- recompiled with patch reverted
- ran same test
This resulted in 100 samples for each setup, 50 from each run. The following is
the output of a t-test for the important variables:
> t.test(d.22$wall, d.22.with.941$wall)
Welch Two Sample t-test
data: d.22$wall and d.22.with.941$wall
t = -0.4932, df = 174.594, p-value = 0.6225
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
-0.011002972 0.006602972
sample estimates:
mean of x mean of y
1.1937 1.1959
> t.test(d.22$user, d.22.with.941$user)
Welch Two Sample t-test
data: d.22$user and d.22.with.941$user
t = -1.5212, df = 197.463, p-value = 0.1298
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
-0.032378364 0.004178364
sample estimates:
mean of x mean of y
1.3335 1.3476
that is to say, it failed to reject the null hypothesis... in less stat-heavy
terms, there's no statistical evidence that this patch makes the test any
slower.
> Datanode xceiver protocol should allow reuse of a connection
> ------------------------------------------------------------
>
> Key: HDFS-941
> URL: https://issues.apache.org/jira/browse/HDFS-941
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: data-node, hdfs client
> Affects Versions: 0.22.0
> Reporter: Todd Lipcon
> Assignee: bc Wong
> Fix For: 0.22.0
>
> Attachments: 941.22.txt, 941.22.txt, 941.22.v2.txt, 941.22.v3.txt,
> HDFS-941-1.patch, HDFS-941-2.patch, HDFS-941-3.patch, HDFS-941-3.patch,
> HDFS-941-4.patch, HDFS-941-5.patch, HDFS-941-6.22.patch, HDFS-941-6.patch,
> HDFS-941-6.patch, HDFS-941-6.patch, fix-close-delta.txt, hdfs-941.txt,
> hdfs-941.txt, hdfs-941.txt, hdfs-941.txt, hdfs941-1.png
>
>
> Right now each connection into the datanode xceiver only processes one
> operation.
> In the case that an operation leaves the stream in a well-defined state (eg a
> client reads to the end of a block successfully) the same connection could be
> reused for a second operation. This should improve random read performance
> significantly.
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