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From "Rohan Pasalkar (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-5711) Removing memory limitation of the Namenode by persisting Block - Block location mappings to disk.
Date Fri, 10 Jan 2014 00:38:51 GMT

     [ https://issues.apache.org/jira/browse/HDFS-5711?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Rohan Pasalkar updated HDFS-5711:

    Issue Type: Sub-task  (was: Improvement)
        Parent: HDFS-2362

> Removing memory limitation of the Namenode by persisting Block - Block location mappings
to disk.
> -------------------------------------------------------------------------------------------------
>                 Key: HDFS-5711
>                 URL: https://issues.apache.org/jira/browse/HDFS-5711
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>            Reporter: Rohan Pasalkar
> This jira is to track changes to be made to remove HDFS name-node memory limitation to
hold block - block location mappings.
> It is a known fact that the single Name-node architecture of HDFS has scalability limits.
The HDFS federation project alleviates this problem by using horizontal scaling. This helps
increase the throughput of metadata operation and also the amount of data that can be stored
in a Hadoop cluster.
> The Name-node stores all the filesystem metadata in memory (even in the federated architecture),
> Name-node design can be enhanced by persisting part of the metadata onto secondary storage
and retaining 
> the popular or recently accessed metadata information in main memory. This design can
benefit a HDFS deployment
> which doesn't use federation but needs to store a large number of files or large number
of blocks. Lin Xiao from Hortonworks attempted a similar
> project [1] in the Summer of 2013. They used LevelDB to persist the Namespace information
(i.e file and directory inode information).
> A patch with this change is yet to be submitted to code base. We also intend to use LevelDB
to persist metadata, and plan to 
> provide a complete solution, by not just persisting  the Namespace information but also
the Blocks Map onto secondary storage. 
> We did implement the basic prototype which stores the block-block location mapping metadata
to the persistent key-value store i.e. levelDB. Prototype also maintains the in-memory cache
of the recently used block-block location mappings metadata. 
> References:
> [1] Lin Xiao, Hortonworks, Removing Name-node’s memory limitation, HDFS-5389, http://www.slideshare.net/ydn/hadoop-meetup-hug-august-2013-removing-the-namenodes-memory-limitation.

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