Hello everyone,

I have configured a Cassandra cluster with 3 nodes, however I am not
getting the write speed that I was expecting. I have tested against a
counter table because it is the bottleneck of the system.
So with the system iddle I run the attached sample code (very simple async
writes with a throttle) against an schema with RF=2 and a table with

The speeds that I get are around 65k updates-writes/second and I was hoping
for at least 150k updates-writes/second. Even if I run the test in 2
machines in parallel, the execution is 35k updates-writes/second in each. I
have executed the test in the nodes themselves (1 and 2 of the 3 nodes).

The nodes are fairly powerful. Each has the following configuration running
Cassandra 3.11.1
- RAM: 256GB
- HDD Disks: 9 (7 configured for cassandra data, 1 for the OS and 1
configured for cassandra commits)
- CPU: 8 processors with hyperthreading => 16 processors

The RAM, CPU and HDDs are far from being maxed out when running the tests.

The test command line class uses two parameters: max executions and
parallelism. Parallelism is the max number of AsyncExecutions running in
parallel. Any other execution will have to wait for available slots.
I tried increasing the parallelism (64, 128, 256...) but the results are
the same, 128 seems enough.

Table definition:

CREATE TABLE counttest (
   key_column bigint,
   cluster_column int,
   count1_column counter,
   count2_column counter,
   count3_column counter,
   count4_column counter,
   count5_column counter,
   PRIMARY KEY ((key_column),cluster_column)

Write test data generation (from the class attached). Each insert is
prepared with uniform random values from below:
            long key_column = getRandom(0, 5000000);
            int cluster_column = getRandom(0, 4096);
            long count1_column = getRandom(0, 10);
            long count2_column = getRandom(0, 10);
            long count3_column = getRandom(0, 10);
            long count4_column = getRandom(0, 10);
            long count5_column = getRandom(0, 10);

*I suspect that we took the wrong approach when designing the hardware:
Should we have used more nodes and less drives per node? If this is the
case, I am trying to understand why or if there is any change that we could
do to the configuration (other than getting more nodes) to improve that.*

Will an SSD dedicated for the commit log improve things dramatically?

Best Regards,

Attachment: testClass.java
Description: Binary data

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