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https://issues.apache.org/jira/browse/PIG-40?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12547917
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Sam Pullara commented on PIG-40:
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The particular notification that I use in my example is evaluated right after a
garbage collection occurs, it should be very accurate.
1) If you want to keep in the old code for a case where you find a VM that
doesn't support that seems fine to me. That said, it worked on Mac (Sun &
soylatte) and Linux (Sun & Jrockit). Haven't tested it on Windows but I can't
imagine Sun failed to implement it there.
2) Rechecking periodically doesn't seem that bad to me. In fact there is a
polling version of this in the javadocs:
https://java.sun.com/j2se/1.5.0/docs/api/java/lang/management/MemoryPoolMXBean.html
though I would always use the 'Collected' thresholds so you don't get false
positives.
I was actually pleasantly surprised to find such great support for doing this
stuff in the VM -- somehow I had missed it in the release notes or at least
forgot to check it out.
> Memory management in BigDataBag is probably wrong
> -------------------------------------------------
>
> Key: PIG-40
> URL: https://issues.apache.org/jira/browse/PIG-40
> Project: Pig
> Issue Type: Bug
> Components: impl
> Reporter: Sam Pullara
> Attachments: BigDataBag.java, MemoryUsage.java
>
>
> src/org/apache/pig/data/BigDataBag.java
> 1) You should not use finalizers for things other than external resources --
> using them here is very dangerous and could inadvertantly lead to deadlocks
> and object resurrection and just decreases performance without any advantage.
> 2) Using .freeMemory() the way it is used in this class is broken.
> freeMemory() is going to return a mostly random number between 0 and the real
> amount. Adding gc() in here is a terrible performance burden. If you really
> want to do something like this you should using softreferences and
> finalization queues.
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