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https://issues.apache.org/jira/browse/HDFS-1114?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12862118#action_12862118
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Tsz Wo (Nicholas), SZE commented on HDFS-1114:
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The data structure we need in BlocksMap is a GettableSet.
{code}
/**
* A set which supports the get operation.
* @param <E> The type of the elements.
*/
public interface GettableSet<E> extends Iterable<E> {
/**
* @return the size of this set.
*/
int size();
/**
* @return true if the given element equals to a stored element.
* Otherwise, return false.
*/
boolean contains(Object element);
/**
* @return the stored element if there is any. Otherwise, return null.
*/
E get(Object element);
/**
* Add the given element to this set.
* @return the previous stored element if there is any.
* Otherwise, return null.
*/
E add(E element);
/**
* Remove the element from the set.
* @return the stored element if there is any. Otherwise, return null.
*/
E remove(Object element);
}
{code}
> Reducing NameNode memory usage by an alternate hash table
> ---------------------------------------------------------
>
> Key: HDFS-1114
> URL: https://issues.apache.org/jira/browse/HDFS-1114
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: name-node
> Reporter: Tsz Wo (Nicholas), SZE
> Assignee: Tsz Wo (Nicholas), SZE
>
> NameNode uses a java.util.HashMap to store BlockInfo objects. When there are
> many blocks in HDFS, this map uses a lot of memory in the NameNode. We may
> optimize the memory usage by a light weight hash table implementation.
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