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From "Chao Shi (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CRUNCH-246) HFileSource
Date Fri, 09 Aug 2013 05:30:48 GMT

    [ https://issues.apache.org/jira/browse/CRUNCH-246?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13734413#comment-13734413
] 

Chao Shi commented on CRUNCH-246:
---------------------------------

Besides the reason that Ryan mentioned about HLog, another pitfall I can think of is multiple
versioned key values. To solve this in raw MR is not that simple, one has to shuffle on keys,
and only keep the one with latest timestamp and handle deletion properly. This is not straightforward
unless the user can understand the internal data structure of HBase, and not simple as it
may result in cascaded MRs if the user logic require a reduce on different key.

But things are different in the crunch world, because we can hide this logic in a utility
method, e.g. HFileUtils.readHFilesThenDedup (anyone has better name?)

[~rbrush] could you please post your HFileInputFormat here, so that I can implement a wrapper
for crunch as well as the utility method described above?
                
> HFileSource
> -----------
>
>                 Key: CRUNCH-246
>                 URL: https://issues.apache.org/jira/browse/CRUNCH-246
>             Project: Crunch
>          Issue Type: Improvement
>          Components: IO
>            Reporter: Chao Shi
>            Assignee: Chao Shi
>
> I found this useful when directly perform MR on HFiles. I used it yesterday when copying
a bunch of HFiles to another cluster (where the region layout is different).
> There is no HFileInputFormat provided by HBase, but I found the following from google:
> https://gist.github.com/leifwickland/1120311
> http://blog.csdn.net/kirayuan/article/details/7794402 (Java version of the above. The
webpage is in chinese, but you can see the code)
> I'm not sure if we copy their code directly (copyright issue?). Anyone knows?

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