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https://issues.apache.org/jira/browse/HDFS-5711?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ajith S reassigned HDFS-5711:
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Assignee: Ajith S
> 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
> Assignee: Ajith S
> Priority: Minor
>
> 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), the
> 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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