nodetool setdefaultrf

Cassandra 4.1+

This command is available in Cassandra 4.1 and later.

Sets the default replication factor used by NetworkTopologyStrategy auto-expansion.

Synopsis

nodetool [connection_options] setdefaultrf <replication_factor>

See connection options for connection options.

Description

nodetool setdefaultrf configures the cluster-wide default replication factor that is applied when creating or altering keyspaces using NetworkTopologyStrategy with the replication_factor shorthand instead of explicit datacenter mappings.

How Auto-Expansion Works

When a keyspace is created using NetworkTopologyStrategy with the generic replication_factor parameter, Cassandra automatically expands this to all known datacenters:

-- Using replication_factor shorthand
CREATE KEYSPACE my_keyspace WITH replication = {
    'class': 'NetworkTopologyStrategy',
    'replication_factor': 3
};

-- Cassandra expands this to explicit datacenter mappings:
-- 'dc1': 3, 'dc2': 3, 'dc3': 3 (for all datacenters in the cluster)

The value set by setdefaultrf becomes the default when replication_factor is not explicitly specified in the CQL statement.

Arguments

Argument	Description
`replication_factor`	The default replication factor to apply. Must be a positive integer.

When to Use

Standardizing Replication Across Teams

In multi-tenant or multi-team environments, setting a cluster-wide default ensures new keyspaces follow organizational standards without requiring explicit specification:

# Set production standard of RF=3
nodetool setdefaultrf 3

This prevents accidental creation of under-replicated keyspaces when developers omit explicit replication settings.

Preparing for Cluster Expansion

Before adding new datacenters, set the default RF to ensure auto-expansion applies the correct replication factor:

# Before adding dc3 to the cluster
nodetool setdefaultrf 3

# When dc3 joins, keyspaces using auto-expansion will include dc3 with RF=3

Automation and Infrastructure-as-Code

When using automation tools that create keyspaces, setdefaultrf provides a safety net:

# Ensure minimum replication regardless of script defaults
nodetool setdefaultrf 3

Behavior Details

Node-Level Setting

This setting is per-node and is not persisted across restarts. Each node in the cluster maintains its own default RF value. For consistent behavior:

Run the command on all nodes
Or configure default_keyspace_rf in cassandra.yaml for persistence

Does Not Affect Existing Keyspaces

Changing the default RF does not alter existing keyspaces. It only affects:

New keyspaces created with replication_factor shorthand
ALTER KEYSPACE commands using replication_factor shorthand

Interaction with Explicit Settings

Explicit datacenter settings always override the default:

-- DC1 gets RF=5, DC2 uses the default from setdefaultrf (e.g., 3)
CREATE KEYSPACE mixed_rf WITH replication = {
    'class': 'NetworkTopologyStrategy',
    'replication_factor': 3,
    'dc1': 5
};

Examples

Set Default RF to Production Standard

nodetool setdefaultrf 3

Verify the Setting

nodetool getdefaultrf

Output:

Applying Across All Nodes

# Run on each node or use parallel execution
for host in node1 node2 node3; do
    ssh "$host" "nodetool setdefaultrf 3"
done

Best Practices

Recommendations

Set on all nodes - The setting is per-node; ensure consistency across the cluster
Use with cassandra.yaml - For persistence, also configure default_keyspace_rf in cassandra.yaml
Match node count - The default RF should not exceed the number of nodes in the smallest datacenter
Production standard: RF=3 - Provides fault tolerance for one node failure while maintaining QUORUM availability

Limitations

Does not affect keyspaces created with explicit datacenter mappings
Does not retroactively change existing keyspaces
Resets to default (1) on node restart unless configured in cassandra.yaml

The persistent equivalent in cassandra.yaml:

# Default replication factor for auto-expanding keyspaces
default_keyspace_rf: 3

Command	Relationship
getdefaultrf	View current default RF
describecluster	View cluster topology and datacenter information
status	Check node count per datacenter

Keyspace DDL - Creating and altering keyspaces
Replication - Replication concepts and strategies