nodetool disablehintsfordc

Disables hints for a specific datacenter.

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Synopsis

nodetool [connection_options] disablehintsfordc <datacenter>

See connection options for connection options.

Description

nodetool disablehintsfordc prevents the local node from storing hints for writes destined for nodes in a specific datacenter. This is useful when a datacenter is expected to be unavailable for an extended period or is being decommissioned.

Non-Persistent Setting

This setting is applied at runtime only and does not persist across node restarts. After a restart, hints for all datacenters are enabled unless configured otherwise in cassandra.yaml.

To permanently disable hints for a datacenter, add it to the hinted_handoff_disabled_datacenters list in cassandra.yaml:

hinted_handoff_disabled_datacenters:
    - dc2

Consistency Impact

Disabling hints for a datacenter means writes to unavailable nodes in that DC will not be recovered automatically. Use nodetool repair to restore consistency after re-enabling.

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Arguments

Argument	Description
datacenter	Name of the datacenter to disable hints for

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Examples

Disable Hints for a Datacenter

nodetool disablehintsfordc dc2

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When to Use

Datacenter Decommissioning

Prevent hint accumulation for a DC being removed:

# Disable hints for DC being decommissioned
nodetool disablehintsfordc dc_old

# Proceed with decommission operations

Extended Datacenter Outage

When a DC will be down longer than the hint window:

# DC2 will be down for extended maintenance
nodetool disablehintsfordc dc2

# Hints would expire anyway, this prevents accumulation

Disk Space Management

Prevent hints from consuming disk when a DC is unavailable:

# Check current hint usage
nodetool tablestats system.hints

# Disable hints for unavailable DC
nodetool disablehintsfordc dc2

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Cluster-Wide Operation

Disable on All Nodes

Hints are stored on coordinator nodes, so disable on all:

disable_hints_dc_cluster.sh

#!/bin/bash
DATACENTER="$1"

if [ -z "$DATACENTER" ]; then
    echo "Usage: $0 <datacenter>"
    exit 1
fi

# Get list of node IPs from local nodetool status
nodes=$(nodetool status | grep "^UN" | awk '{print $2}')

echo "Disabling hints for $DATACENTER on all nodes..."
for node in $nodes; do
    echo -n "$node: "
    ssh "$node" "nodetool disablehintsfordc $DATACENTER" && echo "disabled" || echo "FAILED"
done

echo ""
echo "Remember to re-enable with: nodetool enablehintsfordc $DATACENTER"

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Impact Assessment

Immediate Effects

Aspect	Impact
New hints for DC	Not stored
Existing hints	Continue delivery attempts
Coordinator disk	Stops growing for this DC

Consistency Implications

Scenario	With Hints	Without Hints
DC temporarily down	Auto-recovery	Needs repair
Node restart	Hints delivered	Needs repair
Network partition	Hints queued	Data diverges

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Workflow: Datacenter Maintenance

dc_maintenance_workflow.sh

#!/bin/bash
DC_NAME="$1"

echo "=== Datacenter Maintenance: $DC_NAME ==="

# 1. Disable hints for the DC via SSH
echo "1. Disabling hints for $DC_NAME..."
for node in $(nodetool status | grep "^UN" | awk '{print $2}'); do
    ssh "$node" "nodetool disablehintsfordc $DC_NAME" 2>/dev/null
done

# 2. Log the action
echo "$(date): Hints disabled for $DC_NAME" >> /var/log/cassandra/dc_maintenance.log

# 3. Remind about re-enabling
echo ""
echo "Hints disabled for $DC_NAME"
echo "After maintenance, run:"
echo "  - nodetool enablehintsfordc $DC_NAME (on all nodes)"
echo "  - nodetool repair -dc $DC_NAME"

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Troubleshooting

Hints Still Growing After Disable

# Verify disabled on all coordinators
# Must run on every node in the cluster

# Check if hints are from before disable
nodetool listpendinghints

Wrong Datacenter Name

# List available datacenters
nodetool status | grep "Datacenter:" | awk '{print $2}'

# Use exact name (case-sensitive)

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Recovery After Extended Disable

recover_after_dc_maintenance.sh

#!/bin/bash
DC_NAME="$1"

echo "=== Recovery After DC Maintenance ==="

# 1. Re-enable hints via SSH
echo "1. Re-enabling hints for $DC_NAME..."
for node in $(nodetool status | grep "^UN" | awk '{print $2}'); do
    ssh "$node" "nodetool enablehintsfordc $DC_NAME" 2>/dev/null
done

# 2. Run repair
echo ""
echo "2. Running repair for $DC_NAME..."
nodetool repair -dc $DC_NAME

echo ""
echo "Recovery complete."

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Best Practices

Disable Hints Guidelines

1. Disable cluster-wide - Run on all coordinator nodes
2. Document the reason - Log why and when disabled
3. Plan for repair - Schedule repair after re-enabling
4. Set reminders - Don't forget to re-enable

Considerations

• Data consistency relies on repair after re-enabling
• Don't disable indefinitely without reason
• Affects all writes to nodes in that DC
• Must disable on all nodes to be effective

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Related Commands

Command	Relationship
enablehintsfordc	Re-enable hints for a datacenter
disablehandoff	Disable all hinted handoff
listpendinghints	List pending hints
repair	Restore consistency