question

tarikh avatar image
tarikh asked Erick Ramirez commented

Is it recommended to set RF equal to the number of nodes in each DC for system keyspaces?

for a cluster with two DCs, each has 10 nodes, it is a good idea to set RF to 10 per DC for system schemas?

consideration is to have high availability to connect to it.

will it cause overhead?

ALTER KEYSPACE system_auth WITH REPLICATION = {'class' : 'NetworkTopologyStrategy', 'DC1': '10', 'DC2': 10'};

ALTER KEYSPACE system_distributed WITH REPLICATION = {'class' : 'NetworkTopologyStrategy', 'DC1': '10', 'DC2': 10'};

ALTER KEYSPACE system_traces WITH REPLICATION = {'class' : 'NetworkTopologyStrategy', 'DC1': '10', 'DC2': 10'};

replication
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1 Answer

Erick Ramirez avatar image
Erick Ramirez answered Erick Ramirez commented

The quick answer is no. As a general rule, we recommend 3 replicas in each DC and this rule applies in almost all cases.

I've answered a similar question before about system keyspaces in #5024. For the system_auth keyspace, we recommend configuring it with NetworkTopologyStrategy with 3 replicas in each DC. I've worked with hundreds of clusters for hundreds of companies and this is how they have it configured in almost all cases with only a handful of clusters configured with 5 replicas.

The system_distributed keyspace is used to store repair history if you're running with open source Apache Cassandra so there's no real benefit in changing this unless you intend to run reports against previous repair runs.

The system_traces keyspace holds trace data if you have enabled query tracing. By default trace data expires after 24 hours so its replication settings isn't so critical. Unless you are constantly tracing queries, there's also no point in changing the replication settings for this keyspace. Cheers!

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tarikh avatar image tarikh commented ·

thanks you!

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Erick Ramirez avatar image Erick Ramirez ♦♦ tarikh commented ·

Not a problem. Cheers!

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