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Date: Tue, 14 Sep 2010 10:32:35 -0700 (PDT)
From: kannan chandrasekaran <ckannanck@yahoo.com>
Subject: Re: Couple of cache related questions
To: user@cassandra.apache.org
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Thanks a lot Jonathan !!!

Kannan


________________________________
From: Jonathan Ellis <jbellis@gmail.com>
To: user@cassandra.apache.org
Sent: Mon, September 13, 2010 4:47:05 PM
Subject: Re: Couple of cache related questions

On Sun, Sep 12, 2010 at 6:10 PM, kannan chandrasekaran
<ckannanck@yahoo.com> wrote:
>> 1) What determines the amount of memory used per schema ignoring the
>> general
>> overhead to get cassandra up and running?  Is it just the size of the
>> caches
>> for the column Family + the memtable size ?
>
> and the bloom filter and index samples from the sstable files.
>
> Does that mean that cassandra tries to load the index and filter tables in
> memory as well, for each sstable in the keyspace?

it means it loads the bloom filter file, and a sample from the index file.

> Once the final memtable is flushed to the disk ( assuming no more writes) ,
> does read path also incur the memory size of the memtable for that
> particular CF ?

no.

> Does cassandra try to preallocate memory after startup for each schema even
> if its not used ( not being currently written to or read from)  ?

no.

> If I understand you correctly then I need to make sure that
>  the sum of sizes of all items in the cache across all the keyspaces +
> memtable + bloom filter + index samples  < Heap space

yes.

-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of Riptano, the source for professional Cassandra support
http://riptano.com


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<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:arial,helvetica,sans-serif;font-size:12pt"><div>Thanks a lot Jonathan !!!<br><br>Kannan<br></div><div style="font-family: arial,helvetica,sans-serif; font-size: 12pt;"><br><div style="font-family: arial,helvetica,sans-serif; font-size: 13px;"><font face="Tahoma" size="2"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> Jonathan Ellis &lt;jbellis@gmail.com&gt;<br><b><span style="font-weight: bold;">To:</span></b> user@cassandra.apache.org<br><b><span style="font-weight: bold;">Sent:</span></b> Mon, September 13, 2010 4:47:05 PM<br><b><span style="font-weight: bold;">Subject:</span></b> Re: Couple of cache related questions<br></font><br>
On Sun, Sep 12, 2010 at 6:10 PM, kannan chandrasekaran<br>&lt;<a ymailto="mailto:ckannanck@yahoo.com" href="mailto:ckannanck@yahoo.com">ckannanck@yahoo.com</a>&gt; wrote:<br>&gt;&gt; 1) What determines the amount of memory used per schema ignoring the<br>&gt;&gt; general<br>&gt;&gt; overhead to get cassandra up and running?&nbsp; Is it just the size of the<br>&gt;&gt; caches<br>&gt;&gt; for the column Family + the memtable size ?<br>&gt;<br>&gt; and the bloom filter and index samples from the sstable files.<br>&gt;<br>&gt; Does that mean that cassandra tries to load the index and filter tables in<br>&gt; memory as well, for each sstable in the keyspace?<br><br>it means it loads the bloom filter file, and a sample from the index file.<br><br>&gt; Once the final memtable is flushed to the disk ( assuming no more writes) ,<br>&gt; does read path also incur the memory size of the memtable for that<br>&gt; particular CF ?<br><br>no.<br><br>&gt; Does cassandra
 try to preallocate memory after startup for each schema even<br>&gt; if its not used ( not being currently written to or read from)&nbsp; ?<br><br>no.<br><br>&gt; If I understand you correctly then I need to make sure that<br>&gt; &nbsp;the sum of sizes of all items in the cache across all the keyspaces +<br>&gt; memtable + bloom filter + index samples&nbsp; &lt; Heap space<br><br>yes.<br><br>-- <br>Jonathan Ellis<br>Project Chair, Apache Cassandra<br>co-founder of Riptano, the source for professional Cassandra support<br><span><a target="_blank" href="http://riptano.com">http://riptano.com</a></span><br></div></div>
</div><br>

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