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From Yan Chunlu <springri...@gmail.com>
Subject Re: do I need to add more nodes? minor compaction eat all IO
Date Mon, 25 Jul 2011 13:17:27 GMT
as the wiki suggested:
http://wiki.apache.org/cassandra/LargeDataSetConsiderations
Adding nodes is a slow process if each node is responsible for a large
amount of data. Plan for this; do not try to throw additional hardware
at a cluster at the last minute.


I really would like to know what's the status of my cluster, if it is normal


On Mon, Jul 25, 2011 at 8:59 PM, Yan Chunlu <springrider@gmail.com> wrote:
> I am using normal SATA disk,  actually I was worrying about whether it
> is okay if every time cassandra using all the io resources?
> further more when is the good time to add more nodes when I was just
> using normal SATA disk and with 100r/s it could reach 100 %util....
>
> how large the data size it should be on each node?
>
>
> below is my iostat -x 2 when doing node repair, I have to repair
> column family separately otherwise the load will be more crazy:
>
> Device:         rrqm/s   wrqm/s     r/s     w/s    rMB/s    wMB/s
> avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
> sda               1.50     1.50  121.50   14.00     3.68     0.30
> 60.19   116.98 1569.46   59.49 14673.86   7.38 100.00
>
>
>
>
>
>
> On Sun, Jul 24, 2011 at 8:04 AM, Jonathan Ellis <jbellis@gmail.com> wrote:
>> On Sat, Jul 23, 2011 at 4:16 PM, Francois Richard <frichard@xobni.com> wrote:
>>> My understanding is that during compaction cassandra does a lot of non sequential
readsa then dumps the results with a big sequential write.
>>
>> Compaction reads and writes are both sequential, and 0.8 allows
>> setting a MB/s to cap compaction at.
>>
>> As to the original question "do I need to add more machines" I'd say
>> that depends more on whether your application's SLA is met, than what
>> % io util spikes to.
>>
>> --
>> Jonathan Ellis
>> Project Chair, Apache Cassandra
>> co-founder of DataStax, the source for professional Cassandra support
>> http://www.datastax.com
>>
>

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