Thanks a lot for your reply guys. I was trying fsyn = batch and window =0ms to see if the disk utilization is happening full on my drive. I checked the  numbers using iostat the numbers were around 60% and the CPU usage was also not too high. 

Configuration of my Setup :-

I have three m1.xlarge hosts each having 15 GB RAM and 4 CPU. It has 8 EC2 Compute Units.
I have kept the replication factor equal to 3. The typical write size is 1 KB. 

I tried adding different nodes each with 200 threads and the throughput got split into two. If i do it from a single host with FSync Set to Periodic and Window Size equal to 1000ms and using two nodes i am getting these numbers :-

[OVERALL], Throughput(ops/sec), 4771
[INSERT], AverageLatency(us), 18747
[INSERT], MinLatency(us), 1470
[INSERT], MaxLatency(us), 446413
[INSERT], 95thPercentileLatency(ms), 55
[INSERT], 99thPercentileLatency(ms), 167

[OVERALL], Throughput(ops/sec), 4678
[INSERT], AverageLatency(us), 22015
[INSERT], MinLatency(us), 1439
[INSERT], MaxLatency(us), 466149
[INSERT], 95thPercentileLatency(ms), 62
[INSERT], 99thPercentileLatency(ms), 171

Is there something i am doing wrong in cassandra Setup ?? What is the bet Setup for Cassandra to get high throughput and good write latency numbers ?

On Tue, Jul 17, 2012 at 7:02 AM, Sylvain Lebresne <> wrote:
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.


On Tue, Jul 17, 2012 at 3:43 PM, horschi <> 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.


On Tue, Jul 17, 2012 at 6:13 AM, Code Box <> 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 45.9657130 1.71242    
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 19701.17 1851Q

Are these numbers expected numbers or does Cassandra perform better ? Am i missing something ?