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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-3602) BatchScanner optimization for AccumuloInputFormat
Date Fri, 10 Apr 2015 18:21:13 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-3602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14490051#comment-14490051
] 

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

Github user echeipesh commented on a diff in the pull request:

    https://github.com/apache/accumulo/pull/25#discussion_r28168170
  
    --- Diff: core/src/main/java/org/apache/accumulo/core/client/mapreduce/AccumuloMultiTableInputFormat.java
---
    @@ -86,15 +87,8 @@ public boolean nextKeyValue() throws IOException, InterruptedException
{
           }
     
           @Override
    -      protected void setupIterators(TaskAttemptContext context, Scanner scanner, String
tableName, RangeInputSplit split) {
    -        List<IteratorSetting> iterators = split.getIterators();
    -        if (null == iterators) {
    -          iterators = getInputTableConfig(context, tableName).getIterators();
    -        }
    -
    -        for (IteratorSetting setting : iterators) {
    -          scanner.addScanIterator(setting);
    -        }
    +      protected List<IteratorSetting> contextIterators(TaskAttemptContext context,
String tableName) {
    +        return getInputTableConfig(context, tableName).getIterators();
    --- End diff --
    
    I notice that `mapred.MultiTableInputFormat` does not have similar logic but just uses
Reader from `InputFormatBase` which appears to assume there is only one table target:
    https://github.com/apache/accumulo/blob/master/core/src/main/java/org/apache/accumulo/core/client/mapred/AccumuloMultiTableInputFormat.java#L68
    
    I am not sure if this is a bug, as it looks like, or there is some reason for this.


> 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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