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https://issues.apache.org/jira/browse/HADOOP-803?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12469924
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Raghu Angadi commented on HADOOP-803:
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> Even after a name node starts up, a block in inode does not share the object
> with blockMap.
> So a name node contains two Block instantiations per block.
In the patch, when a file is closed, we do use the reference in blockMap
(because, datanode that has block would have informed namenode already).
Yes, we can get rid of one of blockMap and activeBlocks maps (not both). This
also removes extra block object we have for files that exist before namenode
restarts. The changes for this are a bit more intrusive, I am wondering if I
should do it as part of this patch..
> Reducing memory consumption on Namenode : Part 1
> ------------------------------------------------
>
> Key: HADOOP-803
> URL: https://issues.apache.org/jira/browse/HADOOP-803
> Project: Hadoop
> Issue Type: Bug
> Components: dfs
> Reporter: Raghu Angadi
> Assigned To: Raghu Angadi
> Fix For: 0.12.0
>
> Attachments: block-refs-2.patch, block-refs-3.patch,
> block-refs-5.patch, HADOOP-803-2.patch, HADOOP-803.patch, HADOOP-803_3.patch,
> HADOOP-803_4.patch, NameNodeMemoryHogs.txt
>
>
> There appears to be some places in Namenode that allow reducing memory
> consumption without intrusive code or feature changes. This bug is an initial
> attempt making those changes. Please include your thoughts as well.
> One change I am planning to make :
> Currently one copy of each block exists for each of the replicas and one copy
> for blockMap. I think they are all supposed to be same.
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