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From Kant Kodali <>
Subject Re: Attached profiled data but need help understanding it
Date Wed, 01 Mar 2017 03:51:45 GMT
Hi Romain,

Thanks again. My response are inline.


On Tue, Feb 28, 2017 at 10:04 AM, Romain Hardouin <>

> > we are currently using 3.0.9.  should we use 3.8 or 3.10
> No, don't use 3.X in production unless you really need a major feature.
> I would advise to stick to 3.0.X (i.e. 3.0.11 now).
> You can backport CASSANDRA-11966 easily but of course you have to deploy
> from source as a prerequisite.

  * By backporting you mean I should cherry pick CASSANDRA-11966 commit and
compile from source?*

> > I haven't done any tuning yet.
> So it's a good news because maybe there is room for improvement
> > Can I change this on a running instance? If so, how? or does it require
> a downtime?
> You can throttle compaction at runtime with "nodetool
> setcompactionthroughput". Be sure to read all nodetool commmands, some of
> them are really useful for a day to day tuning/management.
> If GC is fine, then check other things -> "[...] different pool sizes for
> NTR, concurrent reads and writes, compaction executors, etc. Also check if
> you can improve network latency (e.g. VF or ENA on AWS)."
> Regarding thread pools, some of them can be resized at runtime via JMX.
> > 5000 is the target.
> Right now you reached 1500. Is it per node or for the cluster?
> We don't know your setup so it's hard to say it's doable. Can you provide
> more details? VM, physical nodes, #nodes, etc.
> Generally speaking LWT should be seldom used. AFAIK you won't achieve
> 10,000 writes/s per node.
> Maybe someone on the list already made some tuning for heavy LWT workload?

*    1500 total cluster.  *

*    I have a 8 node cassandra cluster. Each node is AWS m4.xlarge instance
(so 4 vCPU, 16GB, 1Gbit network=125MB/s)*

*    I have 1 node (m4.xlarge) for my application which just inserts a
bunch of data and each insert is an LWT     I tested the network throughput
of the node.  I can get up 98 MB/s.*

*    Now, when I start my application. I see that Cassandra nodes Receive
rate/ throughput is about 4MB/s (yes it is in Mega Bytes. I checked this by
running sudo iftop -B). The Disk I/O is also same and the Cassandra process
CPU usage is about 360% (the max is 400% since it is a 4 core machine). The
application node transmission throughput is about 6MB/s. so even with 4MB/s
receive throughput at Cassandra node the CPU is almost maxed out. I am not
sure what this says about Cassandra? But, what I can tell is that Network
is way underutilized and that 8 nodes are unnecessary so we plan to bring
it down to 4 nodes except each node this time will have 8 cores. All said,
I am still not sure how to scale up from 1500 writes/sec? *

> Best,
> Romain

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