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From Mohit Anchlia <>
Subject Re: Reduce Cassandra GC
Date Sat, 15 Jun 2013 19:44:51 GMT
Can you paste you gc config? Also can you take a heap dump at 2 diff points so that we can
compare it?

Quick thing to do would be to do a histo live at 2 points and compare

Sent from my iPhone

On Jun 15, 2013, at 6:57 AM, Takenori Sato <> wrote:

> > INFO [ScheduledTasks:1] 2013-04-15 14:00:02,749 (line 122) GC for
ParNew: 338798 ms for 1 collections, 592212416 used; max is 1046937600
> This says GC for New Generation took so long. And this is usually unlikely. 
> The only situation I am aware of is when a fairly large object is created, and which
can not be promoted to Old Generation because it requires such a large *contiguous* memory
space that is unavailable at the point in time. This is called promotion failure. So it has
to wait until concurrent collector collects a large enough space. Thus you experience stop
the world. But I think it is not stop the world, but only stop the new world.
> For example in case of Cassandra, a large number of in_memory_compaction_limit_in_mb
can cause this. This is a limit when a compaction compacts(merges) rows of a key into the
latest in memory. So this creates a large byte array up to the number.
> You can confirm this by enabling promotion failure GC logging in the future, and by checking
compactions executed at that point in time.
> On Sat, Jun 15, 2013 at 10:01 AM, Robert Coli <> wrote:
>> On Fri, Jun 7, 2013 at 12:42 PM, Igor <> wrote:
>> > If you are talking about 1.2.x then I also have memory problems on the idle
>> > cluster: java memory constantly slow grows up to limit, then spend long time
>> > for GC. I never seen such behaviour for 1.0.x and 1.1.x, where on idle
>> > cluster java memory stay on the same value.
>> If you are not aware of a pre-existing JIRA, I strongly encourage you to :
>> 1) Document your experience of this.
>> 2) Search for anything that sounds similar.
>> 3) If you are unable to find a JIRA, file one.
>> Thanks!
>> =Rob

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