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https://issues.apache.org/jira/browse/HDFS-8555?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15047286#comment-15047286
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Mingliang Liu commented on HDFS-8555:
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Would you kindly explain more by "... only those blocks which belong to
Nicholas out of a given large block."?
And in the _Description_ example, why seek and position read are not able to
return "those blocks that potentially have those 10 lines?"
Thanks.
> Random read support on HDFS files using Indexed Namenode feature
> ----------------------------------------------------------------
>
> Key: HDFS-8555
> URL: https://issues.apache.org/jira/browse/HDFS-8555
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client, namenode
> Affects Versions: 2.5.2
> Environment: Linux
> Reporter: amit sehgal
> Assignee: amit sehgal
> Fix For: 3.0.0
>
> Original Estimate: 720h
> Remaining Estimate: 720h
>
> Currently Namenode does not provide support to do random reads. With so many
> tools built on top of HDFS solving the use case of Exploratory BI and
> providing SQL over HDFS. The need of hour is to reduce the number of blocks
> read for a Random read.
> E.g. extracting say 10 lines worth of information out of 100GB files should
> be reading only those block which can potentially have those 10 lines.
> This can be achieved by adding a tagging feature per block in name node, each
> block written to HDFS will have tags associated to it stored in index.
> Namednode when access via the Indexing feature will use this index native to
> reduce the no. of block returned to the client.
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