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https://issues.apache.org/jira/browse/HIVE-21195?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on HIVE-21195 started by BELUGA BEHR.
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> Review of DefaultGraphWalker Class
> ----------------------------------
>
> Key: HIVE-21195
> URL: https://issues.apache.org/jira/browse/HIVE-21195
> Project: Hive
> Issue Type: Improvement
> Affects Versions: 4.0.0, 3.2.0
> Reporter: BELUGA BEHR
> Assignee: BELUGA BEHR
> Priority: Minor
> Attachments: HIVE-21195.1.patch
>
>
> {code:java}
> protected final List<Node> toWalk = new ArrayList<Node>();
> ...
> while (toWalk.size() > 0) {
> Node nd = toWalk.remove(0);
> {code}
> Every time this loop runs, the first item of a list is removed. For an
> {{ArrayList}}, this means that every time the first item is removed, all of
> the remaining items in the list are copied down one position so that the
> first item is always at array index 0. This is expensive in a tight loop.
> Use a {{Queue}} implementation that does not have this behavior.
> {{ArrayDeque}}
> {quote}
> This class is likely to be faster than Stack when used as a stack, and faster
> than LinkedList when used as a queue.
> {quote}
> https://docs.oracle.com/javase/7/docs/api/java/util/ArrayDeque.html
> Add a little bit extra cleanup since it's being looked at.
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