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From "Lei (Eddy) Xu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9341) Simulated slow disk in SimulatedFSDataset
Date Tue, 01 Dec 2015 23:36:11 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9341?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15034868#comment-15034868

Lei (Eddy) Xu commented on HDFS-9341:

Hi, [~zhz]. Thanks for working on this. This is an interesting patch and it looks good overall.
A few small comments

* {code}
byte readSimulatedByte(Block b, long offsetInBlk, boolean slowness) ;

Should it be private? also {{slowness}} is already a member of {{SimulatedInputStream}}, perhaps
we do not need to pass it here.

* {code}
 SimulatedInputStream(long l, Block b, boolean slow) {
Could you update the comments of {{SimulatedInputStream(...)}} to reflect the parameters.

* {{private boolean randomDiskSlowness;}} should be final.

* Should {{SLOWNESS_PROBABILITY}} and {{SLOWNESS_DELAY_MS }} be configurable? For example,
control "how slow" it is? We can do it in a following JIRA. You mentioned that

bq. The slowness can be random or controlled at certain bytes.

Are you going to implement these features in this patch?

Last, a general question: using {{random}} to build slow I/Os is non-deterministic. Would
it cause problems in unit tests?


> Simulated slow disk in SimulatedFSDataset
> -----------------------------------------
>                 Key: HDFS-9341
>                 URL: https://issues.apache.org/jira/browse/HDFS-9341
>             Project: Hadoop HDFS
>          Issue Type: Test
>          Components: test
>    Affects Versions: 2.7.1
>            Reporter: Zhe Zhang
>            Assignee: Zhe Zhang
>            Priority: Minor
>         Attachments: HDFS-9341.00.patch
> Besides simulating the byte content, {{SimulatedFSDataset}} can also simulate the scenario
where disk is slow when accessing certain bytes. The slowness can be random or controlled
at certain bytes. It can also be made configurable.

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