Hi Marcel,

The RF for that keyspace is currently hardcoded, see CASSANDRA-11098. I am not sure why your RF switched from 1 to 3 after you restarted a cluster, I tried the same and it remained at 1 for me.

The tables in that keyspace are used to store history about the repair operations, having it as RF=3 shouldn't affect the performance of the repair. See CASSANDRA-5839 for when / why it was introduced.
 
Changing the replication from 3 to 1 for system_distributed is not a good idea for the same reasons why changing the replication of any keyspace to 1 is not a good idea. You lose the ability to query that data if a single node goes down.

Hope this helps,

Chris 

On Wed, Jan 8, 2020 at 1:23 AM Marcel Jakobi <maj@ordix.de> wrote:

Hi,

 

the default definition of the keyspace system_distributed is:

CREATE KEYSPACE system_distributed WITH replication = {'class': 'SimpleStrategy', 'replication_factor': '3'}  AND durable_writes = true;

 

 

If I understand correctly, every repair information will be replicated on three servers in the cluster. I have changed the RF to ‚1‘. Once i stop the entire cluster, the replication factor changes again to 3. It seems Cassandra wants it to be 3.

 

Doesn`t that reduce performance on repair operation?

Why is the RF changed again after restart the cluster?

Are there reasons why you shouldn`t change the replication factor to 1?

 

Thanks,

Marcel