nodetool clearsnapshot¶

Removes one or more snapshots from the node to reclaim disk space.

Synopsis¶

nodetool [connection_options] clearsnapshot [options] [--] [keyspace ...]

Description¶

nodetool clearsnapshot deletes snapshot files from the local node. Since snapshots are hard links to SSTable files, they consume disk space when the original SSTables are compacted away. Regular cleanup of old snapshots is essential for disk space management.

Arguments¶

Argument	Description
`keyspace`	Keyspace(s) to clear snapshots from. If omitted, clears from all keyspaces

Options¶

Option	Description
`-t, --tag`	Snapshot tag to clear. Required unless using `--all`
`--all`	Clear all snapshots

Examples¶

Clear Specific Snapshot¶

nodetool clearsnapshot -t my_backup

Removes the snapshot tagged my_backup from all keyspaces.

Clear Snapshot from Specific Keyspace¶

nodetool clearsnapshot -t my_backup my_keyspace

Clear All Snapshots¶

nodetool clearsnapshot --all

Use with Caution

--all removes every snapshot on the node. Verify no critical backups exist before running.

Clear All Snapshots from Keyspace¶

nodetool clearsnapshot --all my_keyspace

When to Use¶

After Successful Backup¶

Once backup files have been copied off-node:

# After copying snapshot files to backup storage
nodetool clearsnapshot -t backup_20240115

Reclaim Disk Space¶

When disk usage is high due to old snapshots:

# Check snapshot sizes first
nodetool listsnapshots

# Remove old snapshots
nodetool clearsnapshot -t old_backup

Clean Up After Testing¶

Remove snapshots created during testing:

nodetool clearsnapshot -t test_snapshot

Regular Maintenance¶

Scheduled cleanup of aged snapshots:

# Find snapshots older than 7 days and clear them
# (Requires scripting based on listsnapshots output)
nodetool clearsnapshot -t weekly_backup_$(date -d "7 days ago" +%Y%m%d)

When NOT to Use¶

Before Verifying Backup¶

Verify Before Clearing

Never clear snapshots until backup files are:

Copied to remote storage
Verified for integrity
Tested for recoverability

On Active Snapshots¶

Don't clear snapshots that are currently being copied or used.

Without Checking First¶

Always list snapshots before clearing:

nodetool listsnapshots

Verification Before Clearing¶

List All Snapshots¶

nodetool listsnapshots

Output:

Snapshot name    Keyspace name    Column family name    True size    Size on disk
backup_20240115  my_keyspace      users                 1.5 GB       1.5 GB
backup_20240115  my_keyspace      orders                2.3 GB       2.3 GB
backup_20240108  my_keyspace      users                 1.2 GB       0 bytes

Check Specific Snapshot¶

nodetool listsnapshots | grep backup_20240115

Verify Disk Usage¶

# Check total snapshot space
du -sh /var/lib/cassandra/data/*/*/snapshots/

# Check specific snapshot
du -sh /var/lib/cassandra/data/*/*/snapshots/backup_20240115/

Space Reclamation¶

How Space is Freed¶

State	SSTable	Snapshot	Disk Usage
Before clearsnapshot	Active (new)	Hard link exists	Space shared via inode
After clearsnapshot	Active (new)	Deleted	Space freed if no other references

Space Reclamation

Hard links are removed by clearsnapshot
Disk blocks are freed only if no other references exist
Space reclamation may not be immediate depending on filesystem

Verifying Space Freed¶

# Before
df -h /var/lib/cassandra

# Clear snapshot
nodetool clearsnapshot -t old_backup

# After
df -h /var/lib/cassandra

Automated Cleanup¶

Script for Aged Snapshots¶

#!/bin/bash
# Clear snapshots older than specified days

DAYS_OLD=7
KEYSPACE="my_keyspace"

# List snapshots and filter by age
nodetool listsnapshots | while read line; do
    # Parse snapshot name and check date
    # Implementation depends on naming convention
done

Using TTL Snapshots (4.0+)¶

Instead of manual cleanup, create snapshots with TTL:

# Snapshot auto-deletes after 24 hours
nodetool snapshot -t temp_backup --ttl 24h my_keyspace

Common Issues¶

"Snapshot does not exist"¶

ERROR: Snapshot 'my_backup' does not exist

The snapshot tag wasn't found:

# List actual snapshot names
nodetool listsnapshots

Space Not Freed¶

If disk space doesn't decrease after clearing:

Check if files were actually removed:

ls /var/lib/cassandra/data/*/*/snapshots/

Hard links may still exist (original SSTable not yet compacted)
Filesystem may not report freed space immediately

Cannot Delete Snapshot Directory¶

Permission issues:

# Check ownership
ls -la /var/lib/cassandra/data/my_keyspace/users-*/snapshots/

# Cassandra user should own files
sudo chown -R cassandra:cassandra /var/lib/cassandra/data/

Best Practices¶

Snapshot Cleanup Guidelines

List before clearing - Verify which snapshots exist
Use specific tags - Avoid --all in production
Verify backups first - Ensure data is safely stored elsewhere
Automate cleanup - Use TTL or scheduled scripts
Monitor disk usage - Track snapshot growth over time
Document retention - Define snapshot retention policies

Retention Policy Example¶

Snapshot Type	Retention
Pre-maintenance	24 hours after maintenance
Daily backup	7 days
Weekly backup	30 days
Monthly backup	1 year

Command	Relationship
snapshot	Create snapshots
listsnapshots	List existing snapshots
tablestats	Check snapshot space per table