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From "Stephen Durfey (JIRA)" <>
Subject [jira] [Commented] (CRUNCH-588) Modify HFileUtils to flex on affected regions for hfiles, rather than all regions
Date Wed, 20 Jan 2016 18:41:40 GMT


Stephen Durfey commented on CRUNCH-588:

{quote}For getting region start key probably want to code against HTableInterface or HBaseAdmin[1]
vs HTable as it'll make changes for the "master" branch easier.{quote}
Can you clarify this? HFileUtils in master passes around an HTable currently. 

{quote}For each family (lines 362-366) we re-calculate the region keys. Is it that expense
or think we should just spin through family filtered KVs once and use those splits for all
I changed this to be more in line with what HFileUtils in master is doing, and that is [sorting
everything up front, and then filtering in the loop over families. 

{quote}On lines 504-505: I'm not seeing how we guarantee the start keys do not get repeated.
Would using something like distinct to eliminate duplicates make sense?{quote}
I was thinking of using a HashSet after the materialize to remove duplicates, and copying
that into a List during the return. 

> Modify HFileUtils to flex on affected regions for hfiles, rather than all regions
> ---------------------------------------------------------------------------------
>                 Key: CRUNCH-588
>                 URL:
>             Project: Crunch
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Stephen Durfey
>            Assignee: Josh Wills
>         Attachments: hfileutils_0.8.5.patch
> HFileUtils when preparing for writing HFiles sets the [number of reducers |]
equal to the number of regions in the table, and then writes out the start keys for each region
to a sequence file for the TotalOrderPartitioner to consume when partitioning data. This can
result in a very large quantity of reducers that don't do anything due to not having any data
to write to hfiles for the region its partition belonged to. 
> My proposal is to modify HFileUtils, with an optional parameter (or a config, that's
up for debate) to determine which regions data will be loaded into ahead of time, and set
the number of reducers to equal the number of regions, and only write out the start keys for
those affected regions. 
> I have working code to do this on the 0.8.x branch of crunch, as that is what I am currently
on. I can modify it to work on more recent versions, but I wanted to start a discussion around
the viability of this code being contributed back to the community. I am still in process
of capturing metrics around the impact of the change (and trying to get data large enough
to test this out), but at least from a reducer count I have seen substantial drops in my limited
testing so far. For example, I had a job go from 705 reduce tasks during the write down to
36 reduce tasks. 
> I've attached what I have so far as of 0.8.4. I'm going to start working on a version
modified for the latest version of crunch. 

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