Mailing-List: contact user-help@cassandra.apache.org; run by ezmlm
Precedence: bulk
Reply-To: user@cassandra.apache.org
Received-SPF: neutral (nike.apache.org: local policy)
MIME-Version: 1.0
In-Reply-To: <tencent_4831712655F302BD1F61E714@qq.com>
References: <tencent_4831712655F302BD1F61E714@qq.com>
Date: Mon, 18 Jun 2012 12:20:31 -0400
Message-ID: 
 <CAKYY9AKtXMtcNjnh8byjbT=H5-7xfw6ftO+yRedk-aXUJ1TV8Q@mail.gmail.com>
Subject: Re: What determines the memory that used by key cache??
From: Jim Ancona <jim@anconafamily.com>
To: user@cassandra.apache.org
Content-Type: multipart/alternative; boundary=e89a8ff252227d3c6d04c2c18b51

--e89a8ff252227d3c6d04c2c18b51
Content-Type: text/plain; charset=UTF-8

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

--e89a8ff252227d3c6d04c2c18b51
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

On Mon, Jun 18, 2012 at 8:53 AM, mich.hph <span dir=3D"ltr">&lt;<a href=3D"=
mailto:mich.hph@gmail.com" target=3D"_blank">mich.hph@gmail.com</a>&gt;</sp=
an> wrote:<br><div class=3D"gmail_quote"><blockquote class=3D"gmail_quote" =
style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>Dear all!</div>
<div>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 calc=
ulate the value. </div></blockquote><div><br>According to=20
<a href=3D"http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com=
/Calculate-memory-used-for-keycache-tp6170528p6170814.html">http://cassandr=
a-user-incubator-apache-org.3065146.n2.nabble.com/Calculate-memory-used-for=
-keycache-tp6170528p6170814.html</a> the formula is:<br>

<br>
key cache memory use =3D <br>
=C2=A0=C2=A0=C2=A0=C2=A0 &lt;Keycache size&gt; * (&lt;8 bytes for position =
i.e. value&gt; +=20
&lt;X bytes for key&gt; + &lt;16 bytes for token (RP)&gt; + &lt;8 byte=20
reference for DecoratedKey&gt; + &lt;8 bytes for descriptor=20
reference&gt;)<br>
which simplifies to <br>
=C2=A0=C2=A0=C2=A0=C2=A0 &lt;Keycache size&gt; * (&lt;key size in bytes&gt;=
 + 40)<br>
<br>Are your row keys 152 bytes?<br><br>Jim<br><br></div><blockquote class=
=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rg=
b(204,204,204);padding-left:1ex">
<div>=C2=A0</div>
<div>Thanks in advance.</div></blockquote></div><br>

--e89a8ff252227d3c6d04c2c18b51--