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https://issues.apache.org/jira/browse/ACCUMULO-3602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14486053#comment-14486053
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ASF GitHub Bot commented on ACCUMULO-3602:
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Github user keith-turner commented on the pull request:
https://github.com/apache/accumulo/pull/25#issuecomment-91038638
> Agreed, but is this a new issue?
I think the intent of this PR is new. I think the intent is to efficiently
support a map reduce job that reads from many small ranges. If we are going to
do that, then lets do it in a way that scales better.
> However, I still think that for many things, it's probably better to
simply use an iterator with some filter criteria.
This approach would work well for existing input format. The only drawback
to this approach is it requires adding custom iterators to tservers classpaths.
The batch scanner approach allows efficient reads of many small ranges from a
tablet w/o custom iterators. Just need a custom function in the map reduce job
to generate the ranges.
> BatchScanner optimization for AccumuloInputFormat
> -------------------------------------------------
>
> Key: ACCUMULO-3602
> URL: https://issues.apache.org/jira/browse/ACCUMULO-3602
> Project: Accumulo
> Issue Type: Improvement
> Components: client
> Affects Versions: 1.6.1, 1.6.2
> Reporter: Eugene Cheipesh
> Assignee: Eugene Cheipesh
> Labels: performance
> Fix For: 1.7.0
>
>
> Currently {{AccumuloInputFormat}} produces a split for reach {{Range}}
> specified in the configuration. Some table indexing schemes, for instance
> z-order geospacial index, produce large number of small ranges resulting in
> large number of splits. This is specifically a concern when using
> {{AccumuloInputFormat}} as a source for Spark RDD where each Split is mapped
> to an RDD partition.
> Large number of small RDD partitions leads to poor parallism on read and high
> overhead on processing. A desirable alternative is to group ranges by tablet
> into a single split and use {{BatchScanner}} to produce the records. Grouping
> by tablets is useful because it represents Accumulos attempt to distributed
> stored records and can be influance by the user through table splits.
> The grouping functionality already exists in the internal {{TabletLocator}}
> class.
> Current proposal is to modify {{AbstractInputFormat}} such that it generates
> either {{RangeInputSplit}} or {{MultiRangeInputSplit}} based on a new setting
> in {{InputConfigurator}}. {{AccumuloInputFormat}} would then be able to
> inspect the type of the split and instantiate an appropriate reader.
> The functinality of {{TabletLocator}} should be exposed as a public API in
> 1.7 as it is useful for optimizations.
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