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From Sylvain Lebresne <sylv...@datastax.com>
Subject Re: Cassandra Evaluation/ Benchmarking: Throughput not scaling as expected neither latency showing good numbers
Date Tue, 17 Jul 2012 14:02:40 GMT
FSync = Batch and Window = 0ms is expected to give relatively crappy
result. It means C* will fsync on disk pretty much all write. This is an
overly safe setting and no database with that kind of setting will perform
correctly because you're far too much bound by the hard drive.

If you want strong local durability, use Batch (so that C* never ack a
non-fsynced write) but keep a bigger window. And in any case, Periodic will
give you better results and provided you use a replication factor > 1, it
is good enough in 99% of the case.

As for the exact numbers, you didn't even say what kind of instance you are
using, nor the replication factor, nor the typical size of each write, so
it's hard to tell you if it seems reasonable or not.

As for the scalability, as horschi said, it's about adding nodes, not
adding clients.

--
Sylvain


On Tue, Jul 17, 2012 at 3:43 PM, horschi <horschi@gmail.com> wrote:

> When they say "linear scalibility" they mean "throughput scales with the
> amount of machines in your cluster".
>
> Try adding more machines to your cluster and measure the thoughput. I'm
> pretty sure you'll see linear scalibility.
>
> regards,
> Christian
>
>
>
> On Tue, Jul 17, 2012 at 6:13 AM, Code Box <codeithere@gmail.com> wrote:
>
>>  I am doing Cassandra Benchmarking using YCSB for evaluating the best
>> performance for my application which will be both read and write intensive.
>> I have set up a three cluster environment on EC2 and i am using YCSB in the
>> same availability region as a client. I have tried various combinations of
>> tuning cassandra parameters like FSync ( Setting to batch and periodic ),
>> Increasing the number of rpc_threads, increasing number of concurrent reads
>> and concurrent writes, write consistency one and Quorum i am not getting
>> very great results and also i do not see a linear graph in terms of
>> scalability that is if i increase the number of clients i do not see an
>> increase in the throughput.
>>
>> Here are some sample numbers that i got :-
>>
>> *Test 1:-  Write Consistency set to Quorum Write Proportion = 100%.
>> FSync = Batch and Window = 0ms*
>>
>> ThreadsThroughput ( write per sec ) Avg Latency (ms)TP95(ms) TP99(ms)
>> Min(ms)Max(ms)
>>
>>
>>  102149 3.1984 51.499291   100 4070 23.82870 2.2260    2004151 45.96571301.7
>> 1242     300419764.68 1154222.09 216
>>
>>
>> If you look at the numbers the number of threads do not increase the
>> throughput. Also the latency values are not that great. I am using fsync
>> set to batch and with 0 ms window.
>>
>> *Test 2:- ** Write Consistency set to Quorum Write Proportion = 100%.
>> FSync = Periodic and Window = 1000 ms*
>> *
>> *
>> 1803 1.23712 1.012312.9Q 10015944 5.343925 1.21579.1Q 200196309.047 1970
>> 1.17 1851Q
>> Are these numbers expected numbers or does Cassandra perform better ? Am
>> i missing something ?
>>
>
>

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