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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Forcing Cassandra to free up some space
Date Thu, 26 May 2011 20:51:01 GMT
I've read the relevant source. While you're pedantically correct re
the spec, you're wrong as to what the JVM actually does.

On Thu, May 26, 2011 at 3:14 PM, Jeffrey Kesselman <jeffpk@gmail.com> wrote:
> Some references...
>
> "An object enters an unreachable state when no more strong references
> to it exist. When an object is unreachable, it is a candidate for
> collection. Note the wording: Just because an object is a candidate
> for collection doesn't mean it will be immediately collected. The JVM
> is free to delay collection until there is an immediate need for the
> memory being consumed by the object."
>
> http://java.sun.com/docs/books/performance/1st_edition/html/JPAppGC.fm.html#998394
>
> and "Calling the gc method suggests that the Java Virtual Machine
> expend effort toward recycling unused objects"
>
> http://download.oracle.com/javase/6/docs/api/java/lang/System.html#gc()
>
> It goes on to say that the VM will make a "best effort", but "best
> effort" is *deliberately* left up to the definition of the gc
> implementor.
>
> I guess you missed the many lectures I have given on this subject over
> the years at Java One Conferences....
>
> On Thu, May 26, 2011 at 3:53 PM, Jonathan Ellis <jbellis@gmail.com> wrote:
>> It's a common misunderstanding that system.gc is only a suggestion; on
>> any VM you're likely to run Cassandra on, System.gc will actually
>> invoke a full collection.
>>
>> On Thu, May 26, 2011 at 2:18 PM, Jeffrey Kesselman <jeffpk@gmail.com> wrote:
>>> Actually this is no gaurantee.   Its a common misunderstanding that
>>> System.gc "forces" gc.  It does not. It is a suggestion only. The vm always
>>> has the option as to when and how much it gcs
>>>
>>> On May 26, 2011 2:51 PM, "Jonathan Ellis" <jbellis@gmail.com> wrote:
>>>
>>
>>
>>
>> --
>> Jonathan Ellis
>> Project Chair, Apache Cassandra
>> co-founder of DataStax, the source for professional Cassandra support
>> http://www.datastax.com
>>
>
>
>
> --
> It's always darkest just before you are eaten by a grue.
>



-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support
http://www.datastax.com

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