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https://issues.apache.org/jira/browse/HDFS-6930?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14115839#comment-14115839
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Arpit Agarwal commented on HDFS-6930:
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The lazyWriter also removes replicas from RAM disk when RAM disk free spaces
falls below one of the two watermarks:
# Less than 10% free space
# Insufficient space for 3 default length blocks.
Eviction is always done immediately after saving blocks, since only saved
blocks become eligible for eviction.
Saving/eviction could potentially still be bursty since it is timer-based. We
could make it behave more smoothly in the future.
> Improve replica eviction from RAM disk
> --------------------------------------
>
> Key: HDFS-6930
> URL: https://issues.apache.org/jira/browse/HDFS-6930
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode
> Affects Versions: HDFS-6581
> Reporter: Arpit Agarwal
> Attachments: HDFS-6930.01.patch
>
>
> The current replica eviction scheme is inefficient since it performs multiple
> file operations in the context of block allocation.
> A better implementation would be asynchronous eviction when free space on RAM
> disk falls below a low watermark to make block allocation faster.
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