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https://issues.apache.org/jira/browse/HDFS-13762?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16736010#comment-16736010
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Wei Zhou commented on HDFS-13762:
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Hi [~rakeshr], thank you very much for reviewing the patch and the great
comments!
??Is the MaxLockedMemory limit applicable to all the "pmemVolumes" together???
Yes, it's a limitation for all the volumes together.
??will it maintain any indexing or just do random search??
We maintains the map from block file to cache-file on pmem storage, so no need
to search for it among the volumes.
??Is there any automatic eviction logic available once volume reaches threshold
or will it throw VolumeFullException to the users??
We don't have a evict logic here or throw a VolumeFullException, it just works
like the memory-cache for compatible now.
For (ii) and (iii), we will update the patch accordingly, thank you very much!
> Support non-volatile storage class memory(SCM) in HDFS cache directives
> -----------------------------------------------------------------------
>
> Key: HDFS-13762
> URL: https://issues.apache.org/jira/browse/HDFS-13762
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: caching, datanode
> Reporter: Sammi Chen
> Assignee: Wei Zhou
> Priority: Major
> Attachments: HDFS-13762.000.patch, HDFS-13762.001.patch,
> HDFS-13762.002.patch, HDFS-13762.003.patch, HDFS-13762.004.patch,
> HDFS-13762.005.patch, HDFS-13762.006.patch, HDFS-13762.007.patch,
> SCMCacheDesign-2018-11-08.pdf, SCMCacheTestPlan.pdf
>
>
> No-volatile storage class memory is a type of memory that can keep the data
> content after power failure or between the power cycle. Non-volatile storage
> class memory device usually has near access speed as memory DIMM while has
> lower cost than memory. So today It is usually used as a supplement to
> memory to hold long tern persistent data, such as data in cache.
> Currently in HDFS, we have OS page cache backed read only cache and RAMDISK
> based lazy write cache. Non-volatile memory suits for both these functions.
> This Jira aims to enable storage class memory first in read cache. Although
> storage class memory has non-volatile characteristics, to keep the same
> behavior as current read only cache, we don't use its persistent
> characteristics currently.
>
>
>
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