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Posted to user@cassandra.apache.org by "mich.hph" <mi...@gmail.com> on 2012/06/18 14:53:32 UTC

What determines the memory that used by key cache??

Dear all!
 In my cluster, I found every key needs 192bytes in the key cache.So I want to know what determines the memory that used by key cache. How to calculate the value. 
  
 Thanks in advance.

Re: What determines the memory that used by key cache??

Posted by Jim Ancona <ji...@anconafamily.com>.

On Mon, Jun 18, 2012 at 8:53 AM, mich.hph <mi...@gmail.com> wrote:

> Dear all!
> In my cluster, I found every key needs 192bytes in the key cache.So I want
> to know what determines the memory that used by key cache. How to calculate
> the value.
>

According to
http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/Calculate-memory-used-for-keycache-tp6170528p6170814.htmlthe
formula is:

key cache memory use =
     <Keycache size> * (<8 bytes for position i.e. value> + <X bytes for
key> + <16 bytes for token (RP)> + <8 byte reference for DecoratedKey> + <8
bytes for descriptor reference>)
which simplifies to
     <Keycache size> * (<key size in bytes> + 40)

Are your row keys 152 bytes?

Jim


> Thanks in advance.
>