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From "Colin Patrick McCabe (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-3290) Use a better local directory layout for the datanode
Date Wed, 18 Apr 2012 20:24:40 GMT

     [ https://issues.apache.org/jira/browse/HDFS-3290?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Colin Patrick McCabe updated HDFS-3290:
---------------------------------------

    Description: 
When the HDFS DataNode stores chunks in a local directory, it currently puts all of the chunk
files into either one big directory, or a collection of directories.  However, there is no
way to know which directory a given block will end up in, given its ID.  As the number of
files increases, this does not scale well.

Similar to the git version control system, HDFS should create a few different top level directories
keyed off of a few bits in the chunk ID.  Git uses 8 bits.  This substantially cuts down on
the number of chunk files in the same directory and gives increased performance, while not
compromising O(1) lookup of chunks.

  was:
When the HDFS DataNode stores chunks in a local directory, it currently puts all of the chunk
files into one big directory.  As the number of files increases, this does not work well at
all.  Local filesystems are not optimized for the case where there are hundreds of thousands
of files in the same directory.  It also makes inspecting directories with standard UNIX tools
difficult.

Similar to the git version control system, HDFS should create a few different top level directories
keyed off of a few bits in the chunk ID.  Git uses 8 bits.  This substantially cuts down on
the number of chunk files in the same directory and gives increased performance.

    
> Use a better local directory layout for the datanode
> ----------------------------------------------------
>
>                 Key: HDFS-3290
>                 URL: https://issues.apache.org/jira/browse/HDFS-3290
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 0.23.0
>            Reporter: Colin Patrick McCabe
>            Assignee: Colin Patrick McCabe
>            Priority: Minor
>
> When the HDFS DataNode stores chunks in a local directory, it currently puts all of the
chunk files into either one big directory, or a collection of directories.  However, there
is no way to know which directory a given block will end up in, given its ID.  As the number
of files increases, this does not scale well.
> Similar to the git version control system, HDFS should create a few different top level
directories keyed off of a few bits in the chunk ID.  Git uses 8 bits.  This substantially
cuts down on the number of chunk files in the same directory and gives increased performance,
while not compromising O(1) lookup of chunks.

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