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From aaron morton <aa...@thelastpickle.com>
Subject Re: Cassandra 0.7.8 and 0.8.1 fail when major compaction on 37GB database
Date Mon, 25 Jul 2011 22:32:09 GMT
How much memory you need depends on a few things such as how many CF's you have, what your
data is like, and what the usage patterns are like. There is no exact formula. 

Generally…
* i would say 4GB of JVM heap is a good start
* key and row caches are set when the CF is created, see "help create column family" in cassandra-cli
* CF sizes are set using when running create column family, BUT under 0.8 there is a new automagical
memory management see http://thelastpickle.com/2011/05/04/How-are-Memtables-measured/
* see the seting in_memory_compaction_limit_in_mb in cassandra.yaml for info on reducing the
memory requirements for compaction. 

The simplest things you can do is increase the JVM heap size to 3 or 4 GB. 

Cheers


-----------------
Aaron Morton
Freelance Cassandra Developer
@aaronmorton
http://www.thelastpickle.com

On 26 Jul 2011, at 00:35, lebron james wrote:

> >There are many things you can do to lower caches,optimize memtables, and tune jvms.
> 
> Please tell what thins i can do   to lower caches,optimize memtables, and tune jvms?
 
> 
> >From experience with similar-sized data sets, 1.5GB may be too little. Recently I
bumped our java HEAP limit from 3GB to 4GB to get ?>past an OOM doing a major compaction.
> 
> In future i need database more than 10TB, so i need solve problem with ram, bacause i
need use not more that 4 GB ram on 5TB database.
> 


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