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From "Branislav Janosik -T (bjanosik - AAP3 INC at Cisco)" <>
Subject Re: Cluster scaling
Date Wed, 08 Feb 2017 21:43:14 GMT
Hi Jan,

Yes, you are right about the batches, I am working on a correction of the way we use batches,
just like you mentioned. I monitored all those stats and seems that hardware is not he bottleneck.
Thank you for the response and advise!


From: Jan Kesten <>
Reply-To: "" <>
Date: Wednesday, February 8, 2017 at 8:20 AM
To: "" <>
Cc: "" <>
Subject: Re: Cluster scaling

Hi Branislav,

what is it you would expect?

Some thoughts:

Batches are often misunderstood, they work well only if they contain only one partition key
- think of a batch of different sensor data to one key. If you group batches with many partition
keys and/or do large batches this puts high load on the coordinator node with then itself
needs to talk to the nodes holding the partitions. This could explain the scaling you see
in your second try without batches. Keep in mind that the driver supports executeAsync and

Second, put commitlog and data directories on seperate disks when using spindles.

Third, have you monitored iostats and cpustats while running your tests?


Am 08.02.2017 um 16:39 schrieb Branislav Janosik -T (bjanosik - AAP3 INC at Cisco):

Hi all,

I have a cluster of three nodes and would like to ask some questions about the performance.

I wrote a small benchmarking tool in java that mirrors (read, write) operations that we do
in the real project.

Problem is that it is not scaling like it should. The program runs two tests: one using batch
statement and one without using the batch.

The operation sequence is: optional select, insert, update, insert. I run the tool on my server
with 128 threads (# of threads has no influence on the performance),

creating usually 100K resources for testing purposes.

The average results (operations per second) with the use of batch statement are:

Replication Factor = 1       with reading        without reading

                1-node cluster     37K                         46K

                2-node cluster     37K                         47K

                3-node cluster     39K                         70K

Replication Factor = 2       with reading        without reading

                2-node cluster     21K                         40K

                3-node cluster     30K                         48K

The average results (operations per second) without the use of batch statement are:

Replication Factor = 1       with reading        without reading

                1-node cluster     31K                         20K

                2-node cluster     38K                         39K

                3-node cluster     45K                         87K

Replication Factor = 2       with reading        without reading

                2-node cluster     19K                         22K

                3-node cluster     26K                         36K

The Cassandra VMs specs are: 16 CPUs,  16GB and two 32GB of RAM, at least 30GB of disk space
for each node. Non SSD, each VM is on separate physical server.

The code is available here . It can be
built with Maven and then you can use jar in target directory with java -jar target/cassandra-test-1.0-SNAPSHOT-jar-with-dependencies.jar

Thank you for any help.


Jan Kesten,

Tel.: +49 561/4739664-0 FAX: -9 Mobil: +49 160 / 90 98 41 68

enercast GmbH Universitätsplatz 12 D-34127 Kassel HRB15471 Online-Prognosen für erneuerbare Energien

Geschäftsführung: Thomas Landgraf (CEO), Bernd Kratz (CTO), Philipp Rinder (CSO)

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