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From Yiming Sun <yiming....@gmail.com>
Subject Re: key cache size in mb = 0 doesn't work?
Date Tue, 27 Nov 2012 04:22:21 GMT
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 <
andras.szerdahelyi@ignitionone.com> wrote:

>
> SSTables in http://en.wikipedia.org/wiki/Page_cache 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
> )
>
> regards,
> Andras
>
> On 27 Nov 2012, at 04:12, Yiming Sun <yiming.sun@gmail.com> wrote:
>
> > 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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