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https://issues.apache.org/jira/browse/ACCUMULO-3602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14380295#comment-14380295
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Eugene Cheipesh commented on ACCUMULO-3602:
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Alright, 1.7 target it is then. I'll rebase on master.
I'll code up a merged InputSplit to see what it would looks like. My intuition
would be to be cautious and have a specific flag for the use of BatchScanner in
cases when split has more than one range. There is still no way to support
offline and client side scans using BatchScanner, so it doesn't cover all
cases. The logic would be similar to what happens now except the branch will be
on split property rather then split class.
Should it be the default approach when possible? I'm not sure, probably yes.
Locality would be tied to a tablet, which is hosted on one machine, you still
can reap the benefits of several IO threads. The effort on querying the
TabletLocator is spent in either case, so why not use it.
> 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
>
> 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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