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From "Bergquist, Brett" <BBergqu...@canoga.com>
Subject RE: Quetion on out memory usage
Date Wed, 15 Feb 2012 18:59:42 GMT
Thanks for the reply Kristian.  

The ++HeapDumpOnOutOfMemoryError is of no use because up to now, I have not found any tool
that can read the heap dump when the heap is configured to 8Gb.  I have tried with this before.


The stack traces when the " java.lang.OutOfMemoryError: GC overhead limit exceeded" is reported
are in the Derby.log, so it is Derby that is trying to put "more stuff on the heap than what
can fit there".   Note that Derby is running in its own JVM with an 8Gb heap.   The system
actually has 32Gb of physical memory and the app server is constrained to 12Gb.

I am in the process of getting the database back locally onto a test system.  I will probably
turn down the heap size to 2Gb and try the query.  Maybe then a tool can analyze the heap.

Again, I appreciate the response and will post what I find.

Brett

-----Original Message-----
From: Kristian Waagan [mailto:kristian.waagan@oracle.com] 
Sent: Wednesday, February 15, 2012 1:28 PM
To: derby-dev@db.apache.org
Subject: Re: Quetion on out memory usage

On 15.02.2012 18:09, Katherine Marsden wrote:
> On 2/15/2012 8:45 AM, Bergquist, Brett wrote:
< snip>
>>
>> java.lang.OutOfMemoryError: GC overhead limit exceeded
>>
>
> I have not personally encountered the GC overhead limit, but google 
> search indicates it is related to the amount of time spent on garbage 
> collection ("too much") and can be overridden.
> http://www.petefreitag.com/item/746.cfm

I've seen this several times and for practical purposes I have always considered this the
same as "Java heap space": for whatever reason you're trying to put more stuff on the heap
than what can fit there.


< snip>
>>
>> The server is a Oracle M3000 and the Derby engine heap is setup to be 
>> 8Gb.
>>
> For a heap out of memory, I have seen occasional cases where  Derby's 
> estimate of whether it can sort in memory is wrong.   You'd need to 
> look at the plan and do some debugging with the actual query  if you 
> are able to reproduce to find out if that is the case here.
>

Not sure, but the code in impl/store/access/sort/MergeInserter may be relevant and a good
starting point.

If you're debugging this, it may be useful to specify -XX:+HeapDumpOnOutOfMemoryError (and
possibly 
|-XX:HeapDumpPath=/your/dump/path).

|
-- 
Kristian



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