nodetool enablehintsfordc¶

Enables hints for a specific datacenter.

Synopsis¶

nodetool [connection_options] enablehintsfordc <datacenter>

Description¶

nodetool enablehintsfordc re-enables hint storage for nodes in a specific datacenter after it was disabled with disablehintsfordc. When enabled, the local node will store hints for writes destined for unavailable nodes in the specified datacenter.

Arguments¶

Argument	Description
`datacenter`	Name of the datacenter to enable hints for

Examples¶

Enable Hints for a Datacenter¶

nodetool enablehintsfordc dc2

When to Use¶

After Datacenter Recovery¶

Re-enable hints after a datacenter comes back online:

# DC2 is back online
nodetool enablehintsfordc dc2

# Verify hints are being stored again

After Datacenter Maintenance¶

Resume normal hint behavior after planned maintenance:

# Maintenance complete
nodetool enablehintsfordc dc2

# Monitor hint activity
nodetool listpendinghints

Restore Normal Operations¶

Return to default behavior after temporary disable:

# Re-enable hints for datacenter
nodetool enablehintsfordc dc2

# Verify enabled (no specific status command, but hints will accumulate)

Cluster-Wide Operation¶

Enable on All Nodes¶

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

#!/bin/bash
# enable_hints_dc_cluster.sh

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}')

for node in $nodes; do
    echo -n "$node: "
    ssh "$node" "nodetool enablehintsfordc $DATACENTER" && echo "enabled" || echo "FAILED"
done

Use Cases¶

Multi-DC Recovery Workflow¶

#!/bin/bash
# dc_recovery_workflow.sh

DC_NAME="$1"

echo "=== Datacenter Recovery: $DC_NAME ==="

# 1. Verify DC is back online
echo "1. Checking datacenter status..."
nodetool status | grep "$DC_NAME" -A 10

# 2. Re-enable hints for this DC on all nodes via SSH
echo ""
echo "2. 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

# 3. Run repair to restore consistency
echo ""
echo "3. Consider running repair for full consistency"
echo "   nodetool repair -dc $DC_NAME"

Impact¶

When Hints Are Enabled¶

Aspect	Behavior
Hint storage	Resumes for DC
Coordinator disk	May grow with hints
Automatic recovery	Restored
Write guarantees	Full coverage

Troubleshooting¶

Hints Not Being Stored After Enable¶

# Verify datacenter name is correct
nodetool status

# Check if hints are accumulating
nodetool listpendinghints

# Check for errors
grep -i "hint" /var/log/cassandra/system.log | tail -10

Wrong Datacenter Name¶

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

# Use exact datacenter name
nodetool enablehintsfordc <exact_name>

Best Practices¶

Enable Hints Guidelines

Verify DC is healthy - Ensure nodes are UP before enabling
Enable cluster-wide - Run on all coordinator nodes
Monitor after enable - Watch hint accumulation
Consider repair - Run repair for extended outages

Default Behavior

By default, hints are enabled for all datacenters. This command is only needed after explicitly disabling hints for a DC.

Command	Relationship
disablehintsfordc	Disable hints for a datacenter
enablehandoff	Enable all hinted handoff
listpendinghints	List pending hints
statushandoff	Check handoff status