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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-3602) BatchScanner optimization for AccumuloInputFormat
Date Wed, 08 Apr 2015 21:09:12 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-3602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14486048#comment-14486048
] 

ASF GitHub Bot commented on ACCUMULO-3602:
------------------------------------------

Github user ctubbsii commented on the pull request:

    https://github.com/apache/accumulo/pull/25#issuecomment-91037784
  
    In JIRA, I [mentioned][1] "sometimes it's better to query a larger range and let an iterator
filter out non-matching results".
    
    I think the createRanges method @keith-turner  describes could work if the function is
executed in the RecordReader (it also simplifies this issue significantly, because you wouldn't
need to create a new InputSplit type, but simply add an option to the AccumuloInputFormat).
There's still some risk of memory exhaustion with a large number of ranges within a tablet
(especially if the ranges were an exhaustive set of row-records to retrieve).
    
    However, I still think that for many things, it's probably better to simply use an iterator
with some filter criteria. It could be a SkippingIterator that seeks to ranges which are pre-configured
on that iterator, or it could be a Filter which has some filter criteria.
    
    [1]: https://issues.apache.org/jira/browse/ACCUMULO-3602?focusedCommentId=14327767&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14327767


> 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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