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From aaron morton <aa...@thelastpickle.com>
Subject Re: About the heap
Date Thu, 14 Mar 2013 13:27:42 GMT
> Because of this I have an unstable cluster and have no other choice than use Amazon EC2
xLarge instances when we would rather use twice more EC2 Large nodes.
m1.xlarge is a MUCH better choice than m1.large.
You get more ram and better IO and less steal. Using half as many m1.xlarge is the way to
go. 

> My heap is actually changing from 3-4 GB to 6 GB and sometimes growing to the max 8 GB
(crashing the node).
How is it crashing ?
Are you getting too much GC or running OOM ? 
Are you using the default GC configuration ?
Is cassandra logging a lot of GC warnings ?

If you are running OOM then something has to change. Maybe bloom filters, maybe caches.

Enable the GC logging in cassandra-env.sh to check how low a CMS compaction get's the heap,
or use some other tool. That will give an idea of how much memory you are using. 

Here is some background on what is kept on heap in pre 1.2
http://www.mail-archive.com/user@cassandra.apache.org/msg25762.html

Cheers

-----------------
Aaron Morton
Freelance Cassandra Consultant
New Zealand

@aaronmorton
http://www.thelastpickle.com

On 13/03/2013, at 12:19 PM, Wei Zhu <wz1975@yahoo.com> wrote:

> Here is the JIRA I submitted regarding the ancestor.
> 
> https://issues.apache.org/jira/browse/CASSANDRA-5342
> 
> -Wei
> 
> 
> ----- Original Message -----
> From: "Wei Zhu" <wz1975@yahoo.com>
> To: user@cassandra.apache.org
> Sent: Wednesday, March 13, 2013 11:35:29 AM
> Subject: Re: About the heap
> 
> Hi Dean,
> The index_interval is controlling the sampling of the SSTable to speed up the lookup
of the keys in the SSTable. Here is the code:
> 
> https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/db/DataTracker.java#L478
> 
> To increase the interval meaning, taking less samples, less memory, slower lookup for
read.
> 
> I did do a heap dump on my production system which caused about 10 seconds pause of the
node. I found something interesting, for LCS, it could involve thousands of SSTables for one
compaction, the ancestors are recorded in case something goes wrong during the compaction.
But those are never removed after the compaction is done. In our case, it takes about 1G of
heap memory to store that. I am going to submit a JIRA for that. 
> 
> Here is the culprit:
> 
> https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/io/sstable/SSTableMetadata.java#L58
> 
> Enjoy looking at Cassandra code:)
> 
> -Wei
> 
> 
> ----- Original Message -----
> From: "Dean Hiller" <Dean.Hiller@nrel.gov>
> To: user@cassandra.apache.org
> Sent: Wednesday, March 13, 2013 11:11:14 AM
> Subject: Re: About the heap
> 
> Going to 1.2.2 helped us quite a bit as well as turning on LCS from STCS which gave us
smaller bloomfilters.
> 
> As far as key cache.  There is an entry in cassandra.yaml called index_interval set to
128.  I am not sure if that is related to key_cache.  I think it is.  By turning that to 512
or maybe even 1024, you will consume less ram there as well though I ran this test in QA and
my key cache size stayed the same so I am really not sure(I am actually checking out cassandra
code now to dig a little deeper into this property.
> 
> Dean
> 
> From: Alain RODRIGUEZ <arodrime@gmail.com<mailto:arodrime@gmail.com>>
> Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
> Date: Wednesday, March 13, 2013 10:11 AM
> To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
> Subject: About the heap
> 
> Hi,
> 
> I would like to know everything that is in the heap.
> 
> We are here speaking of C*1.1.6
> 
> Theory :
> 
> - Memtable (1024 MB)
> - Key Cache (100 MB)
> - Row Cache (disabled, and serialized with JNA activated anyway, so should be off-heap)
> - BloomFilters (about 1,03 GB - from cfstats, adding all the "Bloom Filter Space Used"
and considering they are showed in Bytes - 1103765112)
> - Anything else ?
> 
> So my heap should be fluctuating between 1,15 GB and 2.15 GB and growing slowly (from
the new BF of my new data).
> 
> My heap is actually changing from 3-4 GB to 6 GB and sometimes growing to the max 8 GB
(crashing the node).
> 
> Because of this I have an unstable cluster and have no other choice than use Amazon EC2
xLarge instances when we would rather use twice more EC2 Large nodes.
> 
> What am I missing ?
> 
> Practice :
> 
> Is there a way not inducing any load and easy to do to dump the heap to analyse it with
MAT (or anything else that you could advice) ?
> 
> Alain
> 
> 


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