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https://issues.apache.org/jira/browse/HDFS-5751?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Arpit Agarwal updated HDFS-5751:
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Summary: Remove the FsDatasetSpi and FsVolumeSpi interfaces (was: Remove
the FsDatasetSpi and FsVolumeImpl interfaces)
> Remove the FsDatasetSpi and FsVolumeSpi interfaces
> --------------------------------------------------
>
> Key: HDFS-5751
> URL: https://issues.apache.org/jira/browse/HDFS-5751
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode, test
> Affects Versions: 3.0.0
> Reporter: Arpit Agarwal
>
> The in-memory block map and disk interface portions of the DataNode have been
> abstracted out into an {{FsDatasetpSpi}} interface, which further uses
> {{FsVolumeSpi}} to represent individual volumes.
> The abstraction is useful as it allows DataNode tests to use a
> {{SimulatedFSDataset}} which does not write any data to disk. Instead it just
> stores block metadata in memory and returns zeroes for all reads. This is
> useful for both unit testing and for simulating arbitrarily large datanodes
> without having to provision real disk capacity.
> A 'real' DataNode uses {{FsDataSetImpl}}. Both {{FsDatasetImpl}} and
> {{SimulatedFSDataset}} implement {{FsDatasetSpi}}.
> However there are a few problems with this approach:
> # Using the factory class significantly complicates the code flow for the
> common case. This makes the code harder to understand and debug.
> # There is additional burden of maintaining two different dataset
> implementations.
> # Fidelity between the two implementations is poor.
> Instead we can eliminate the SPIs and just hide the disk read/write routines
> with a dependency injection framework like Google Guice.
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