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https://issues.apache.org/jira/browse/HDFS-5711?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13860795#comment-13860795
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Ajay commented on HDFS-5711:
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Hi [~sureshms]
Rohan ( [~rohanpasalkar] ) and I ( [~Aj0Ay] ) intend to work on this together.
To clean up the jira - our intention was not to tag along with the umbrella
jira HDFS-2362 [https://issues.apache.org/jira/browse/HDFS-2362]. Please let us
know if we should have a single separate jira to track changes required to
persist all the memory resident metadata and then have subtasks for each
metadata component?
Our intention is to address the issue of persisting the block information (esp.
since Lin Xiao {intern at Hortonworks} had already worked on a prototype to
persist the namespace information), but to design the solution such that the
persistent storage layer could be re-used to persist other NN memory resident
metadata.
> 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: Improvement
> 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), 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,
> http://www.slideshare.net/ydn/hadoop-meetup-hug-august-2013-removing-the-namenodes-memory-limitation
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