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https://issues.apache.org/jira/browse/HDFS-6581?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14141483#comment-14141483
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Andrew Wang commented on HDFS-6581:
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bq. HDFS-4953 is not a subtask of HDFS-4949, and you yourself have said that it
is an independent change.
Arpit, it's unfair to say that HDFS-4953 isn't related to HDFS-4949. ZCR makes
the most sense when it's used in combination with HDFS-4949 which is why we
started working on ZCR in the first place. We committed it to the HDFS-4949
branch first and brought it down to trunk before the rest of the branch because
other people were interested in using the new API.
bq. Also no numbers were cited or provided as evidence when calling the merge
vote for HDFS-4949 so I don't think the community could reasonably be expected
to take that into consideration.
I don't think this is a reasonable conclusion. HDFS-4953 is certainly related
to HDFS-4949, had benchmark results, and was already closely scrutinized by the
community before the merge (37 watchers, including yourself). It didn't seem
necessary to bring it up the performance again in the merge email, and we could
have easily pointed at the existing results on HDFS-4953 if anyone asked for
performance numbers.
I'm trying to be constructive here, which is why I provided a pointer to
HDFS-6287. It's a microbenchmark that can actually read at close to memory
speed (GB/s), which isn't true of a lot of other tests. Setting something up
that writes and then reads using vecsum seems like a reasonable benchmark. Not
sure if you have libhdfs bindings for this work yet, but that'd be the best
thing if you want to adapt vecsum.
> Write to single replica in memory
> ---------------------------------
>
> Key: HDFS-6581
> URL: https://issues.apache.org/jira/browse/HDFS-6581
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Reporter: Arpit Agarwal
> Assignee: Arpit Agarwal
> Attachments: HDFS-6581.merge.01.patch, HDFS-6581.merge.02.patch,
> HDFS-6581.merge.03.patch, HDFS-6581.merge.04.patch, HDFS-6581.merge.05.patch,
> HDFS-6581.merge.06.patch, HDFS-6581.merge.07.patch,
> HDFSWriteableReplicasInMemory.pdf, Test-Plan-for-HDFS-6581-Memory-Storage.pdf
>
>
> Per discussion with the community on HDFS-5851, we will implement writing to
> a single replica in DN memory via DataTransferProtocol.
> This avoids some of the issues with short-circuit writes, which we can
> revisit at a later time.
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