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From "zhangcheng" <zhangch...@jike.com>
Subject Re: Re: Key cache hit rate issue
Date Fri, 17 Feb 2012 02:41:43 GMT
Yes, Cassandra has no way of knowing that all the data is in the most recent sstable, and will
have to check the others too, and this bring a lot of difficulty to data compaction.

I have a question that if  I want a high performance data compaction, how can I implement
that all the columns are all in the most recent sstable, by this, I think the read performace
will be better.




2012-02-17 



zhangcheng 



发件人: Jonathan Ellis 
发送时间: 2012-02-17  10:13:20 
收件人: user 
抄送: 
主题: Re: Key cache hit rate issue 
 
On Thu, Feb 16, 2012 at 3:52 PM, Eran Chinthaka Withana
<eran.chinthaka@gmail.com> wrote:
> Thanks for the reply. Yes there is a possibility that the keys can be
> distributed in multiple SSTables, but my data access patterns are such that
> I always read/write the whole row. So I expect all the data to be in the
> same SSTable (please correct me if I'm wrong).
If you're doing slice reads, Cassandra has no way of knowing that all
the data is in the most recent sstable, and will have to check the
others too.
> For some reason 16637958 (the keys cached) has become a golden number and I
> don't see key cache increasing beyond that.
16637958 is your configured cache capacity according to the cfstats you pasted.
-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support
http://www.datastax.com
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