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From kannan chandrasekaran <>
Subject Re: Cassandra Cache Mbean values; bytes or number of elements ? and row count
Date Sun, 19 Sep 2010 17:21:06 GMT
Thanks again for the replies Jonathan.... Couple more clarifications....

1) Since the sstables are write-once only (append only), does cassandra count 
the updates to the same key as a separate row ...i.e does the row count include 
even the old/deleted data ? 

2) If I need the count of the rows in a columnfamily whats the best way to get 
that information... Is it OK to use the capacity field in the MBean interface to 
get the rowcount for a given columnfamily assuming its exposed as a public API 
and keycache is set to "100%"  or  is this approach a bit too hacky ? 

3) I read about get_range_slices...but it says "Unlike get_key_range, this 
applies the given predicate to all keys in the range, not just those with 
undeleted matching data. ".... Does that mean the api returns even obsolete data 
? Please help me understand this.
4) If you were to use get_range_slices for the row count then the idea is to:
* Use the get_range_slices to fetch all data
* Count the rows at the client side
Correct me if I am wrong ...


From: Jonathan Ellis <>
To: user <>
Sent: Sat, September 18, 2010 2:42:28 AM
Subject: Re: Cassandra Cache Mbean values; bytes or number of elements ?


it gets the capacity from your configuration setting. cassandra knows
how many rows you have, and you told it to cache all of them, so
that's what it set capacity to.

On Fri, Sep 17, 2010 at 8:58 PM, kannan chandrasekaran
<> wrote:
> I am using 0.6.5 and my keycache for the CF is set as "100%" ... What do the
> values in the Mbean interfaces indicate ?  bytes or number of elements ?
> Specifically, these are the numbers that I observe for one of the column
> family...
> capacity = 36826888 (if this is number of elements,  how does cassandra come
> up with this number ?)
> Size = 148834
> Please let me know.
> Thanks
> Kannan

Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of Riptano, the source for professional Cassandra support

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