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https://issues.apache.org/jira/browse/KYLIN-2716?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Zhong Yanghong updated KYLIN-2716:
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Summary: Using non-thread-safe WeakHashMap leading to server high cpu
(was: WeakHashMap in ClassUtil leading to server high cpu and some query
doesn't respond)
> Using non-thread-safe WeakHashMap leading to server high cpu
> ------------------------------------------------------------
>
> Key: KYLIN-2716
> URL: https://issues.apache.org/jira/browse/KYLIN-2716
> Project: Kylin
> Issue Type: Bug
> Components: Query Engine
> Affects Versions: all
> Reporter: Zhong Yanghong
> Assignee: Zhong Yanghong
>
> WeakHashMap is not thread safe, which is used in the method
> *ClassUtil.forName*. It's a high possibility that multiple threads invoke the
> method *ClassUtil.forName* simultaneously leading to a dead loop in
> *WeakHashMap.get() -> getTable() -> expungeStaleEntries()*, which finally
> resulting in server high cpu and some query doesn't respond.
> We made an inner test by invoking the method *ClassUtil.forName* 1M times,
> the result is as follows:
> * With cache: 20ms;
> * Without cache: less than 2s.
> By invoking the method *ClassUtil.forName* with *newInstance* 1M times, the
> result is as follows:
> * With cache: around 2s
> * Without cache: around 3s.
> Considering *ClassUtil.forName* is always invoked with *newInstance*, there's
> no much downgrade without cache. Thus the fix is just to remove the cache.
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