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From Wei Zhu <>
Subject Re: About the heap
Date Wed, 13 Mar 2013 18:35:29 GMT
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:

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:

Enjoy looking at Cassandra code:)


----- Original Message -----
From: "Dean Hiller" <>
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

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.


From: Alain RODRIGUEZ <<>>
Reply-To: "<>" <<>>
Date: Wednesday, March 13, 2013 10:11 AM
To: "<>" <<>>
Subject: About the heap


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) ?


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