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From Gary Tully <>
Subject Re: Memoryleak when consuming messages from KahaDBStore
Date Thu, 19 Feb 2009 09:54:54 GMT
Hi Jörg,
I did some analysis of the per message allocations from your email. It
is clear that each store write allocates a bunch of objects, however,
from code inspection, I cannot see a point where they are leaked
through a reference.
There are two relevant points that may make static analysis a little
difficult. First is the fact that writes are asynchronous, so there
will be a small delay until write allocations are free for GC. This
should be very small in reality though.
Second is that store pages remain in memory until they are pushed out
of a LRU cache, a page has the possibility of referencing batch writes
and indexes with location information, ie: most of the per write
allocated objects.

In short, we need to repeat your experiment with some more depth by
taking caching issues into consideration.  This is on my to do list.

>From a more high level view point, is it the case that a long running
test, with say 2000m/s in and out of the broker will eventually run
out of memory?

I ask this because there are two sequential questions: 1) is there
really a memory leak (long running test gets into trouble) 2) if there
is a leak, where is it?


2009/2/13 Cybexion <>:
> Hello,
> I just tried something with the Netbeans memory profiler.
> My assumption is:
> If nothing hass been added to an application then after 2 full runs of the
> Garbace Collector the memory should be the same.
> In the past we have seen that memory was increasing while messages have been
> processed by AMQ. For me that means that something stays in memory even
> after those messages have been dequeued.
> My test looks like this:
> 1. start a fresh AMQ instance, send some messages to a queue for
> initialisation
> 2. do a full GC
> 3. Take a memory snapshot
> 4. send exactly 1000 message to the queue
> 5. consume all 1000 messages from the queue
> 6. do a full GC
> 7. Take a another memory snapshot
> Assumption:
> I would expect that no references to messages do exist any more in the AMQ
> JVM because they have all been processed. The memory should look more or
> less like it was before the test.
> Now I did a memory comparision of my two snapshots.
> The result looks like this:
> From within the "org.apache.activemq" package there are exactly 1000
> MessageKeys, 1000 RemoveMessageCommands and 1000 AdMessageCommands left
> over.
> Shouldn't those have disappeared because the queue is empty???
> Additionaly, if we look at the "org.apache.kaha" package:
> There are 2000 DataByteArrayOutputstreams, 2000 Location objects and 2000
> WriteCommands still inside the memory. I would also have expected that those
> do not exist after the queue is empty.
> Well, personally this does not help me, but maybe one of the developers can
> convert this information into a possible bug inside the code?
> Help would really be appreciated.
> Thanks
> Jörg
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