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From "Rui Li (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-15527) Memory usage is unbound in SortByShuffler for Spark
Date Wed, 11 Jan 2017 11:14:58 GMT

    [ https://issues.apache.org/jira/browse/HIVE-15527?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15818027#comment-15818027
] 

Rui Li commented on HIVE-15527:
-------------------------------

Hi [~csun], it seems the current solution relies on how the iterators are used - the inner
iterator must be consumed before moving forward the outer iterator. Is there any guarantee
this assumption will hold? Even if it works at the moment, I'm afraid changes in Hive or Spark
can easily break it.

> Memory usage is unbound in SortByShuffler for Spark
> ---------------------------------------------------
>
>                 Key: HIVE-15527
>                 URL: https://issues.apache.org/jira/browse/HIVE-15527
>             Project: Hive
>          Issue Type: Improvement
>          Components: Spark
>    Affects Versions: 1.1.0
>            Reporter: Xuefu Zhang
>            Assignee: Chao Sun
>         Attachments: HIVE-15527.0.patch, HIVE-15527.0.patch, HIVE-15527.1.patch, HIVE-15527.2.patch,
HIVE-15527.3.patch, HIVE-15527.4.patch, HIVE-15527.5.patch, HIVE-15527.6.patch, HIVE-15527.7.patch,
HIVE-15527.patch
>
>
> In SortByShuffler.java, an ArrayList is used to back the iterator for values that have
the same key in shuffled result produced by spark transformation sortByKey. It's possible
that memory can be exhausted because of a large key group.
> {code}
>             @Override
>             public Tuple2<HiveKey, Iterable<BytesWritable>> next() {
>               // TODO: implement this by accumulating rows with the same key into a list.
>               // Note that this list needs to improved to prevent excessive memory usage,
but this
>               // can be done in later phase.
>               while (it.hasNext()) {
>                 Tuple2<HiveKey, BytesWritable> pair = it.next();
>                 if (curKey != null && !curKey.equals(pair._1())) {
>                   HiveKey key = curKey;
>                   List<BytesWritable> values = curValues;
>                   curKey = pair._1();
>                   curValues = new ArrayList<BytesWritable>();
>                   curValues.add(pair._2());
>                   return new Tuple2<HiveKey, Iterable<BytesWritable>>(key,
values);
>                 }
>                 curKey = pair._1();
>                 curValues.add(pair._2());
>               }
>               if (curKey == null) {
>                 throw new NoSuchElementException();
>               }
>               // if we get here, this should be the last element we have
>               HiveKey key = curKey;
>               curKey = null;
>               return new Tuple2<HiveKey, Iterable<BytesWritable>>(key, curValues);
>             }
> {code}
> Since the output from sortByKey is already sorted on key, it's possible to backup the
value iterable using the same input iterator.



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