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https://issues.apache.org/jira/browse/HBASE-20674?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16500753#comment-16500753
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Mike Drob commented on HBASE-20674:
-----------------------------------
One thing that is unclear to me...
If it's a local FS then we will always disable write checksums and verify
checksums, currently. If it is not a local FS, we will only disable verify
checksums on the "nochecksum fs" that we keep around. So we are still writing
the checksums but never reading them? Is there nuance here, that we may decide
to go back and read those checksums? I thought I saw a comment somewhere that
if hbase checksums fail we'll fall back to DFS checksums but I can't locate it
anymore, maybe was my imagination.
Further tidied up the logic in v2 and added additional comments inline.
[~xiaochen] - this is the context of the checksum stuff I was asking you about
earlier. Maybe take a look and tell me if I'm way off base on anything?
> clean up short circuit read logic and docs
> ------------------------------------------
>
> Key: HBASE-20674
> URL: https://issues.apache.org/jira/browse/HBASE-20674
> Project: HBase
> Issue Type: Bug
> Components: regionserver
> Affects Versions: 2.0.0
> Reporter: Mike Drob
> Assignee: Mike Drob
> Priority: Major
> Attachments: HBASE-20674.patch, HBASE-20674.v2.patch
>
>
> Mailing list discussion at
> https://lists.apache.org/thread.html/f6f73df0ceae29f762f9b9088e3ffd0bf8f109d3dd692df100bf4fd6@%3Cdev.hbase.apache.org%3E
> There are several inconsistencies between how our docs claim we do things and
> how we actually do things.
> There are two docs sections that attempt to address how SCR should work.
> dfs.client.read.shortcircuit.skip.checksum is advised to set to true, but our
> code in separate places ignores it and then later sets it to true anyway.
> CommonFSUtils and FSUtils duplicate code related to SCR setup.
> There is a workaround in HFileSystem for a bug that's been fixed in all
> versions of hadoop that we support. (HADOOP-9307)
> We suggest setting dfs.client.read.shortcircuit.buffer.size to a value that
> is very close to what we'd set it to anyway, without clearly explaining why
> this is important.
> There are other properties that we claim are important, but we don't offer
> any suggestions or explanations.
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