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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7661) [umbrella] support hflush and hsync for erasure coded files
Date Thu, 07 Apr 2016 01:32:25 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7661?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15229490#comment-15229490
] 

Todd Lipcon commented on HDFS-7661:
-----------------------------------

I'm not super active on either HDFS or HBase anymore, but Kai asked me to take a look at the
issue, especially with regard to his latest comment. My (slightly ill-informed) opinion is
that he's right -- this sounds like a very complicated feature to get right, and maybe has
minimal benefit. For HBase, the use case for hflush is for the WALs, which typically make
up a vast minority of the disk space usage of the cluster. So, the benefits of EC from a space-savings
perspective are not so large. The benefits from a throughput perspective due to striping sound
enticing at first, but I think it's probably better addressed by the "multi-WAL" feature which
already allows striping at the application level.

So, my gut feel is that for the first EC-supporting release it might be safest to not include
the feature, or to do so only as an experimental feature that has to be enabled by a config
(somewhat like dfs.support.append was, way back in the day when it wasnt super stable).

> [umbrella] support hflush and hsync for erasure coded files
> -----------------------------------------------------------
>
>                 Key: HDFS-7661
>                 URL: https://issues.apache.org/jira/browse/HDFS-7661
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: erasure-coding
>            Reporter: Tsz Wo Nicholas Sze
>            Assignee: GAO Rui
>         Attachments: EC-file-flush-and-sync-steps-plan-2015-12-01.png, HDFS-7661-unitTest-wip-trunk.patch,
HDFS-7661-wip.01.patch, HDFS-EC-file-flush-sync-design-v20160323.pdf, HDFS-EC-file-flush-sync-design-version1.1.pdf,
Undo-Log-Design-20160406.jpg
>
>
> We also need to support hflush/hsync and visible length. 



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