Performance of write requests?

Karsten Thygesen karthy at netic.dk
Tue May 11 13:54:50 EDT 2010


Hi Ryan

I'm running the cluster on 4 physical servers with many cores each so CPU is not a limitation. Regarding the storage, we use Sun Openstorage which essential means, that we are writing to a flashdisk. Besides, I tried to use memorybased filesystem for storage with non significant changes in performance (50% better or so), so I doubt, that IO is my challenge. 

But I have noted the ZFS tuning recommendations - that will come in handy when we go in larger roll out.

But - David Dawson pointed me in the right direction - my simple converter script did a "fetch record, write record, repeat" lifecycle and the bare roundtrip time was a killer.

I have not extended my little script to become multithreaded (each write to the cluster happens in a dedicated thread) and that very simple enhancement now gave me more then 200 writes/sec, so I believe that the bottleneck is in my script and not the RIAK cluster right now.

I have run out of time for today, but I will continue my experiments tomorrow and finetune my script more (read: make it more parallel and perhaps distribute it to more hosts).

Best regards,
Karsten

On May 10, 2010, at 23:46 , Ryan Tilder wrote:

> A couple of quick questions for you Karsten that should help us get an idea of what kind of issues you might be having.
> 
> How many physical hosts are you running the four OpenSolaris virtuals on?  If they're all running on the same host and you don't have a pretty substantial RAID array backing their local storage, you're just going to get I/O contention between the virtuals, slowing down writes.
> 
> There are some ZFS tuning parameters we've found that can improve write throughput.  Since you're using dets there's one in particular that will be helpful.  You can run this command as root on each OpenSolaris virtual:
> 
> zfs atime=off <pool>
> 
> The fact that you can essentially double your performance by running another client in parallel does make me wonder whether or not it might be a mild performance issue with your invocation of the ripple client.  Do you see a linear increase in write performance as you increase the number of parallel writers?
> 
> --Ryan
> 
> On Mon, May 10, 2010 at 8:36 AM, Karsten Thygesen <karthy at netic.dk> wrote:
> Hi
> 
> I'm doing a small proof-of-concept and the goal is to store about 250.000.000 records in a Riak cluster. Today, we have the data in MySQL, but we strive for better performance and we might even expect up to 5 times as mush data during the next couple of years. The data is denormalized and "document" like so they are an easy match for NoSQL paradigm. 
> 
> For the small POC, I have built a 4 node cluster with 4 dedicated virtual servers running Opensolaris on top of VMWare but with quite fast storage below. In fron of the cluster I have a loadbalancer which will distribute reuests evenly among the nodes.
> 
> Each node is running riak-0.10 with almost deafult configuration. I have added "-smp enabled" to vm.args and each node is otherwise using default configuration (except for name of cause). This also implies N=2 and dest for storage backend.
> 
> I have written a small ruby script which uses riak-client from Ripple (latest version) as well as curd for http connections and it quite simple takes each record from the database and stores is in riak. Each record is around 500-1000 bytes large and entirely structured text/data. I store them as JSON objects.
> 
> The script can easily read more than 15.000 records/second, process them and print them to the screen, so I doubt the script is the bottleneck.
> 
> When I try to write them to the riak cluster via the loadbalancer, I can only write around 50-60 records/second and while writing, the beam process is only using  around 10% cpu and no major IO activity is going on.
> 
> I have tried to move the data directory to /tmp (memory filesystem) and with this setup, I can get around 90 write/sec (yes - only for testing - I can not live with memoryfilesystem in production with this dataset).
> 
> I have also noticed, that the performance I get is almost equivalent nomatter if I write through the loadbalancer or I just select a node and sends all my writes to that one. 
> 
> I have also tried a "multithreaded" approach where I simply run two of my datamover scripts in parallel, and that way, I can get around 110 writes/second.
> 
> With the current performance, it will take me more than a month to move my data from mysql to Riak, so I need a multitude of better performance.
> 
> Do you have any suggestions for how to get better performance? I was hoping for towards 1000 writes/second so feel free to speculate - perhaps I should just add quite a bunch of more servers?
> 
> Best regards,
> Karsten
> 
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