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From Jeffrey Kesselman <jef...@gmail.com>
Subject Re: Forcing Cassandra to free up some space
Date Thu, 26 May 2011 20:14:30 GMT
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.

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