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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Couple of cache related questions
Date Mon, 13 Sep 2010 23:47:05 GMT
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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