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From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4949) Centralized cache management in HDFS
Date Sat, 10 Aug 2013 01:09:52 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4949?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13735643#comment-13735643

Arun C Murthy commented on HDFS-4949:

[~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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