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From Andras Szerdahelyi <>
Subject Re: key cache size in mb = 0 doesn't work?
Date Tue, 27 Nov 2012 05:14:03 GMT
If its the RMI horror ( registry port + actual port ) you are worried about, enabling MX4J
in for the HTTP transport (
) could help although i never used it myself. Or you can just throw in the Jolokia JVM agent which will do roughly the same

i'm not aware of the hit rate or any of the other cf/system metrics being exposed over anything
other than JMX, sorry. You can poke around with nodetool on the nodes themselves ( that uses
JMX itself ) to get other metrics, but i have not been able to get cache stats out of nodetool
cfstats. I think it might be because they are no longer on the CF's mbean.


On 27 Nov 2012, at 05:22, Yiming Sun <<>>

Interesting -- I completely overlooked the OS cache aspect, but how long does the OS keep
cached pages? It seems they reside in memory for 4 hours at least (which happens to be the
default time for key cache)..  The CF has over 2.6 million rows, and I am only fetching a
random set of 5000 each time.

Where else can I examine the cache hit ratio? The nodes are remote servers behind some strict
university controlled firewall, so it wouldn't be easy for me to tap in using JConsole.  Thanks.

-- Y.

On Mon, Nov 26, 2012 at 11:06 PM, Andras Szerdahelyi <<>>

SSTables in maybe?
How many rows do you have in this CF? Are you getting all columns?

What do the cassandra.db mbeans say ( hit ratio, cache requests, items etc )


On 27 Nov 2012, at 04:12, Yiming Sun <<>>

> Hi,
> I am carrying out some performance test against a 6-node cassandra cluster (v1.1.0),
and need to disable the key cache entirely as one of the scenarios.
> However, by setting key_cache_size_in_mb to 0, I am still seeing caching effects.  For
example, when I fetch a set of 5000 rows, the first time it would deliver at about 60MB/sec,
but all subsequent fetches (even after fetching several other sets), it would deliver at about
120MB/sec.  This is exactly the same behavior I have observed when the key_cache_size_in_mb
was left blank.
> So I am just wondering how I can disable the key cache entirely.  All our nodes have
JNA.jar deployed -- not sure it this has anything to do with what I saw.  Thanks.
> -- Y

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