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https://issues.apache.org/jira/browse/HBASE-21874?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16769571#comment-16769571
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Vladimir Rodionov edited comment on HBASE-21874 at 2/15/19 6:30 PM:
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This patch requires good write up, it is not clear how this thing work,
[~ram_krish]. From what I see, you extends FileMmapEngine, which works with
persistent cache by mmapping it into RAM, so your new engine does exactly the
same thing? As far as I understand, the major selling point of PMEM is
providing RAM-like capacity beyond what DRAM can do. So we are supposed to have
some relatively small DRAM and large size of NVDIMM installed into a server.
This raises the questions:
# Where are your going to keep bucket cache? Not in DRAM definitely, hence in
NVDIMM (PMEM)?
# If you keep data in PMEM and use extended FileMmapIOEngine, where do yo you
mmap it into? into DRAM? That is strange
# My question, regarding file system required on top PMEM has remained
unanswered.
What I see in this patch (may be I am wrong)
# You rely on file system on top of PMEM
# You mmap PMEM resided file into DRAM
Am I right?
was (Author: vrodionov):
This patch requires good write up, it is not clear how this thing work,
[~ram_krish]. From what I see, you extends FileMmapEngine, which works with
persistent cache by mmapping it into RAM, so your new engine does exactly the
same thing? As far as I understand, the major selling point of PMEM is
providing RAM-like capacity beyond what DRAM can do. So we are supposed to have
some relatively small DRAM and large size of NVDIMM installed into a server.
This raises the questions:
# Where are your going to keep bucket cache? Not in DRAM definitely, hence in
NVDIMM (PMEM)?
# If you keep data in PMEM and use extended FileMmapIOEngine, where do yo you
mmap it into? into DRAM? That is strange
# My question, regarding file system required on top PMEM has remained
unanswered.
What I see in this patch (may be I am wrong)
# You rely on file system on top of PMEM
# You mmap PMEM resided file into DRAM
This does not look right to me.
> Bucket cache on Persistent memory
> ---------------------------------
>
> Key: HBASE-21874
> URL: https://issues.apache.org/jira/browse/HBASE-21874
> Project: HBase
> Issue Type: New Feature
> Components: BucketCache
> Affects Versions: 3.0.0
> Reporter: ramkrishna.s.vasudevan
> Assignee: ramkrishna.s.vasudevan
> Priority: Major
> Fix For: 3.0.0
>
> Attachments: HBASE-21874.patch, HBASE-21874.patch,
> HBASE-21874_V2.patch, Pmem_BC.png
>
>
> Non volatile persistent memory devices are byte addressable like DRAM (for
> eg. Intel DCPMM). Bucket cache implementation can take advantage of this new
> memory type and can make use of the existing offheap data structures to serve
> data directly from this memory area without having to bring the data to
> onheap.
> The patch is a new IOEngine implementation that works with the persistent
> memory.
> Note : Here we don't make use of the persistence nature of the device and
> just make use of the big memory it provides.
> Performance numbers to follow.
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