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https://issues.apache.org/jira/browse/ACCUMULO-3602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14484193#comment-14484193
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ASF GitHub Bot commented on ACCUMULO-3602:
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Github user keith-turner commented on a diff in the pull request:
https://github.com/apache/accumulo/pull/25#discussion_r27926398
--- Diff:
core/src/main/java/org/apache/accumulo/core/client/mapreduce/lib/impl/InputConfigurator.java
---
@@ -517,6 +517,74 @@ public static Boolean isOfflineScan(Class<?>
implementingClass, Configuration co
}
/**
+ * Controls the use of the {@link BatchScanner} in this job.
+ * Using this feature will group ranges by their source tablet per
InputSplit and use BatchScanner to read them.
--- End diff --
Could mention what options this will not work with in javadoc. For example
setting this will not work w/ offline scan and local iters.
Could also mention the benefit of doing this. It seems the main benefit is
one RPC to send multiple ranges to a tserver and then read the results, versus
an RPC per range.
> 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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