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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 16:21:12 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-3602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14485464#comment-14485464
] 

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

Github user keith-turner commented on a diff in the pull request:

    https://github.com/apache/accumulo/pull/25#discussion_r27986006
  
    --- Diff: core/src/main/java/org/apache/accumulo/core/client/mapred/AbstractInputFormat.java
---
    @@ -384,7 +387,21 @@ public static InputTableConfig getInputTableConfig(JobConf job, String
tableName
       protected abstract static class AbstractRecordReader<K,V> implements RecordReader<K,V>
{
         protected long numKeysRead;
         protected Iterator<Map.Entry<Key,Value>> scannerIterator;
    -    protected RangeInputSplit split;
    +    protected org.apache.accumulo.core.client.mapreduce.impl.AccumuloInputSplit split;
    +    protected ScannerBase scannerBase;
    +
    +    /**
    +     * Configures the iterators on a scanner for the given table name.
    +     *
    +     * @param job
    +     *          the Hadoop job configuration
    +     * @param scanner
    +     *          the scanner for which to configure the iterators
    +     * @param tableName
    +     *          the table name for which the scanner is configured
    +     * @since 1.7.0
    +     */
    +    protected abstract void setupIterators(JobConf job, ScannerBase scanner, String tableName,
AccumuloInputSplit split);
    --- End diff --
    
    I like how your suggestion moves configuration of the scanner to a private method.  Trying
to understand your suggestion made me realize I don't understand why `AccumuloInputSplit`
is storing and serializing things like iterators.    Why not get that info from the job conf
when the task runs?  I am being lazy asking this question, let me know if its not quick/easy
to explain I can dig around in the code.


> 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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