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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 6:27 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
This does not look right to me.
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:
1. Where are your going to keep bucket cache? Not in DRAM definitely, hence in
NVDIMM (PMEM)?
2. If you keep data in PMEM and use extended FileMmapIOEngine, where do yo you
mmap it into? into DRAM? That is strange
3. My question, regarding file system required on top PMEM has remained
unanswered.
What I see in this patch (may be I am wrong)
1. You rely on file system on top of PMEM
2. You mmap PMEM resided file into DRAM
This does not look optimal 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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