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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1989) Add support for simulated Data Nodes - helpful for testing and performance benchmarking of the Name Node without having a large cluster
Date Tue, 06 Nov 2007 18:40:50 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1989?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12540526
] 

Doug Cutting commented on HADOOP-1989:
--------------------------------------

> For example startDataNode refers to the simulated impl if it is starting the simulated
fsdataset [ ... ]

This could be handled other ways, that do not require test code in trunk, no?  For example,
you could replace 'new SimulatedFoo' with (FooInterface)ReflectionUtils.newInstance("org.apache.hadoop.dfs.SimulatedFoo"),
so that there's no compile-time dependency.  This could be inside a factory method, so that
it's only done once per simulated class.

> Add support for simulated Data Nodes  - helpful for testing and performance benchmarking
of the Name Node without having a large cluster
> ----------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-1989
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1989
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: dfs
>            Reporter: Sanjay Radia
>            Priority: Minor
>         Attachments: SimulatedStoragePatchSubmit.txt, SimulatedStoragePatchSubmit5.txt
>
>
> Proposal is to add an implementation for a Simulated Data Node.
> This will 
>   - allow one to test certain parts of the system (especially the Name Node, protocols)
much more easily and efficiently.
>   - allow one to run performance benchmarks on the Name node without having a large cluster.
>   - Inject faults for testing (e.g. one can add random faults based probability parameters).
> The idea is that the Simulated Data Node will
>  - discard any data written to blocks (but remember the blocks and their sizes)
>  - generate fixed data on the fly when blocks are read (e.g. block is fixed set of bytes
or repeated sequence of strings).
> The Simulated Data Node can also be used for fault injection.
> The data node can be parameterized with probabilities that allow one to control:
>   - Delays on reads and writes, creates, etc
>   - IO Exceptions
>  - Loss of blocks 
>  - Failures

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