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https://issues.apache.org/jira/browse/HDFS-5851?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14047035#comment-14047035
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Konstantin Shvachko commented on HDFS-5851:
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Few questions as I don't see it covered in the design document:
# Heterogeneous storage is implemented but not enabled, as for now it can only
allocate the StorageType.DEFAULT blocks. This seems to be the first extension
to other StorageTypes. Why memory type is getting prioritized ahead of say SSDs?
# I understand the design assumes that only one DN will hold a memory replica
of a DDM block. This will increase the latency accessing that block for a
single client, but it also makes this DN a bottleneck for many clients trying
to access the same data.
# If I understood correctly the proposal is to not introduce new APIs for
discarding unnecessary or lost data, but handle it using a discardability
policy. What is the policy?
#- In this regard Eric's idea of ZK ephemeral nodes is interesting, but
probably not directly applicable, as a file should not be discarded only
because its creator quit.
# Eviction policy is another thing which needs clarification.
# What do you mean by "static allocation of memory"? A configuration parameter
for DNs?
> Support memory as a storage medium
> ----------------------------------
>
> Key: HDFS-5851
> URL: https://issues.apache.org/jira/browse/HDFS-5851
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: datanode
> Affects Versions: 3.0.0
> Reporter: Arpit Agarwal
> Assignee: Arpit Agarwal
> Attachments:
> SupportingMemoryStorageinHDFSPersistentandDiscardableMemory.pdf,
> SupportingMemoryStorageinHDFSPersistentandDiscardableMemory.pdf,
> SupportingMemoryStorageinHDFSPersistentandDiscardableMemory.pdf
>
>
> Memory can be used as a storage medium for smaller/transient files for fast
> write throughput.
> More information/design will be added later.
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