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From aaron morton <aa...@thelastpickle.com>
Subject Re: key cache size calculation
Date Tue, 03 Apr 2012 01:49:25 GMT
Take a look at the key cache hit rate in nodetool cfstats. 

One approach is to increase the cache size until you do not see a matching increase in the
hit rate. 

> Is there a limit to key cache size? I know that is all taken from heap but how much max
we can go with setting the key cache sizes?

It's pretty much a memory thing. 

Each entry maps a description of the SStable and the key to the offset in the index file.
(off the top of my head) The SSTable description is shared, the row key, row token (16 bytes)
and offset (offset) will take up space.

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

On 3/04/2012, at 11:24 AM, Shoaib Mir wrote:

> Hi guys,
> 
> We are calculating key cache size right now. There is this column family with ~ 100 million
columns and right now we have the cache size set at 2 million.
> 
> I suspect that the active data we got is not all fitting in the 2 million cache size
and we at times are getting query execution time way higher then the normal. Is there a limit
to key cache size? I know that is all taken from heap but how much max we can go with setting
the key cache sizes?
> 
> cheers,
> Shoaib


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