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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-3602) BatchScanner optimization for AccumuloInputFormat
Date Fri, 17 Apr 2015 16:08:59 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-3602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14500103#comment-14500103
] 

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_r28607317
  
    --- Diff: core/src/main/java/org/apache/accumulo/core/client/mapred/AbstractInputFormat.java
---
    @@ -629,32 +676,37 @@ public float getProgress() throws IOException {
             }
             for (Map.Entry<KeyExtent,List<Range>> extentRanges : tserverBin.getValue().entrySet())
{
               Range ke = extentRanges.getKey().toDataRange();
    -          for (Range r : extentRanges.getValue()) {
    -            if (autoAdjust) {
    -              // divide ranges into smaller ranges, based on the tablets
    -              RangeInputSplit split = new RangeInputSplit(tableName, tableId, ke.clip(r),
new String[] {location});
    -
    -              split.setOffline(tableConfig.isOfflineScan());
    -              split.setIsolatedScan(tableConfig.shouldUseIsolatedScanners());
    -              split.setUsesLocalIterators(tableConfig.shouldUseLocalIterators());
    -              split.setMockInstance(mockInstance);
    -              split.setFetchedColumns(tableConfig.getFetchedColumns());
    -              split.setPrincipal(principal);
    -              split.setToken(token);
    -              split.setInstanceName(instance.getInstanceName());
    -              split.setZooKeepers(instance.getZooKeepers());
    -              split.setAuths(auths);
    -              split.setIterators(tableConfig.getIterators());
    -              split.setLogLevel(logLevel);
    -
    -              splits.add(split);
    -            } else {
    -              // don't divide ranges
    -              ArrayList<String> locations = splitsToAdd.get(r);
    -              if (locations == null)
    -                locations = new ArrayList<String>(1);
    -              locations.add(location);
    -              splitsToAdd.put(r, locations);
    +          if (batchScan) {
    +            // group ranges by tablet to be read by a BatchScanner
    +            ArrayList<Range> clippedRanges = new ArrayList<Range>();
    +            for(Range r: extentRanges.getValue())
    --- End diff --
    
    Sorry for confusing you guys, it's actually backwards. BatchScan does essentially the
same thing as AutoAdjust in terms of clipping on tablet boundaries. AutoAdjust is on by default,
so there is no issue. Asking for BatchScan and AutoAdjust off is a nonsensical case.
    
    So I've added mentions in both javadocs as Keith suggested and an exception on AutoAdjust
= false BatchScan = true, since it indicates user specifically asked for something we can
not and know not how to give them.
    
    This is pushed up now.


> 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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