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https://issues.apache.org/jira/browse/HDFS-8401?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14560011#comment-14560011
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Arpit Agarwal commented on HDFS-8401:
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bq. I'm not sure I see the advantage of having a separate file system, rather
than simply putting this into HDFS. bq. Can you clarify how users would
interact with this system?
Colin, our goal is making it easier for applications to use memory support in
HDFS specifically and Hadoop Compatible File Systems in general.
# Allow using memory features without calling HDFS-specific APIs. This also
isolates applications from evolving APIs. Applications currently use shims and
reflection tricks to work with different versions of HDFS.
# Once applications start using memfs someone could write a memfs layer over
another HCFS e.g. Amazon S3.
memfs itself will not cache any data when used with hdfs. wrt interaction,
applications can choose to use {{memfs://}} paths instead of {{hdfs://}} paths
for data targeted to memory.
bq. How does this relate to DDM?
There is no immediate plan to introduce a discardable namespace.
> Memfs - a layered file system for in-memory storage in HDFS
> -----------------------------------------------------------
>
> Key: HDFS-8401
> URL: https://issues.apache.org/jira/browse/HDFS-8401
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: Arpit Agarwal
> Assignee: Arpit Agarwal
>
> We propose creating a layered filesystem that can provide in-memory storage
> using existing features within HDFS. memfs will use lazy persist writes
> introduced by HDFS-6581. For reads, memfs can use the Centralized Cache
> Management feature introduced in HDFS-4949 to load hot data to memory.
> Paths in memfs and hdfs will correspond 1:1 so memfs will require no
> additional metadata and it can be implemented entirely as a client-side
> library.
> The advantage of a layered file system is that it requires little or no
> changes to existing applications. e.g. Applications can use something like
> {{memfs://}} instead of {{hdfs://}} for files targeted to memory storage.
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