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https://issues.apache.org/jira/browse/HDFS-4949?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13735643#comment-13735643
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Arun C Murthy commented on HDFS-4949:
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[~andrew.wang] overall it's looks great, some more questions:
# I'm not sure you want to automatically add new files in a directory to the
cache, it seems a higher-level system (Hive, Impala, HCat) are in better
position. Not doing this automatically simplifies cache mgmt, quota mgmt etc.
# Can you please provide details on the read apis? For the Hive/MR/Pig use case
I'd like to see a new open(Path, offset, length) which returns an indicator for
whether the block is cached or not. This, for e.g., would be used by the
RecordReader to read the split.
> Centralized cache management in HDFS
> ------------------------------------
>
> Key: HDFS-4949
> URL: https://issues.apache.org/jira/browse/HDFS-4949
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: datanode, namenode
> Affects Versions: 3.0.0, 2.3.0
> Reporter: Andrew Wang
> Assignee: Andrew Wang
> Attachments: caching-design-doc-2013-07-02.pdf,
> caching-design-doc-2013-08-09.pdf
>
>
> HDFS currently has no support for managing or exposing in-memory caches at
> datanodes. This makes it harder for higher level application frameworks like
> Hive, Pig, and Impala to effectively use cluster memory, because they cannot
> explicitly cache important datasets or place their tasks for memory locality.
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