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https://issues.apache.org/jira/browse/HDFS-6658?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14062514#comment-14062514
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Colin Patrick McCabe commented on HDFS-6658:
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bq. If we don't have caching, we need to cope with the added latency of
off-heap memory - It is after all backed up by a file.
Amir, there's no file involved. See my comment here:
https://issues.apache.org/jira/browse/HDFS-6658?focusedCommentId=14061374&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14061374
I'm talking about memory. Memory, not disk. It is simply RAM that is not
managed by the JVM. There's more information here:
http://stackoverflow.com/questions/6091615/difference-between-on-heap-and-off-heap.
> Namenode memory optimization - Block replicas list
> ---------------------------------------------------
>
> Key: HDFS-6658
> URL: https://issues.apache.org/jira/browse/HDFS-6658
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Affects Versions: 2.4.1
> Reporter: Amir Langer
> Assignee: Amir Langer
> Attachments: Namenode Memory Optimizations - Block replicas list.docx
>
>
> Part of the memory consumed by every BlockInfo object in the Namenode is a
> linked list of block references for every DatanodeStorageInfo (called
> "triplets").
> We propose to change the way we store the list in memory.
> Using primitive integer indexes instead of object references will reduce the
> memory needed for every block replica (when compressed oops is disabled) and
> in our new design the list overhead will be per DatanodeStorageInfo and not
> per block replica.
> see attached design doc. for details and evaluation results.
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