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https://issues.apache.org/jira/browse/HDFS-4465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13695922#comment-13695922
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Suresh Srinivas commented on HDFS-4465:
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bq. The point there was to save the extra object overhead, since in the DN we
have a 1-to-1 correspondence between BlockScanInfo and Block objects being
created. Given this, do you still want to use containment instead of
inheritance?
The reason I posted that comment was, in HDFS we had heavy and incorrect use of
"is a" relationship, that had resulted in not very clean code. But in this
case, I see that it is justified. Perhaps adding a comment in BlockScanInfo
about why this is done and memory saving would be good.
> Optimize datanode ReplicasMap and ReplicaInfo
> ---------------------------------------------
>
> Key: HDFS-4465
> URL: https://issues.apache.org/jira/browse/HDFS-4465
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Affects Versions: 2.0.5-alpha
> Reporter: Suresh Srinivas
> Assignee: Aaron T. Myers
> Attachments: dn-memory-improvements.patch, HDFS-4465.patch
>
>
> In Hadoop a lot of optimization has been done in namenode data structures to
> be memory efficient. Similar optimizations are necessary for Datanode
> process. With the growth in storage per datanode and number of blocks hosted
> on datanode, this jira intends to optimize long lived ReplicasMap and
> ReplicaInfo objects.
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