nodetool enableautocompaction¶

Re-enables automatic compaction for specified keyspaces and tables.

Synopsis¶

nodetool [connection_options] enableautocompaction [--] [<keyspace> <tables>...]

Description¶

nodetool enableautocompaction restores automatic compaction behavior for one or more tables after it was temporarily disabled with disableautocompaction. When auto-compaction is enabled, Cassandra's compaction strategy continuously evaluates SSTables and triggers compaction operations based on configured thresholds and policies.

Automatic compaction is essential for:

Maintaining read performance - Merging SSTables reduces the number of files to scan
Reclaiming disk space - Removing tombstones and expired data
Data consistency - Ensuring deleted data is eventually purged
Preventing SSTable proliferation - Keeping file counts manageable

Default State

Auto-compaction is enabled by default on all tables. This command is only needed after explicitly disabling it with disableautocompaction.

Arguments¶

Argument	Description
`keyspace`	Target keyspace name. If omitted, applies to all keyspaces
`tables`	Space-separated list of table names. If omitted, applies to all tables in the keyspace

Examples¶

Enable for All Keyspaces and Tables¶

# Re-enable compaction cluster-wide on this node
nodetool enableautocompaction

Enable for Specific Keyspace¶

# Re-enable for all tables in a keyspace
nodetool enableautocompaction my_keyspace

Enable for Specific Tables¶

# Re-enable for specific tables only
nodetool enableautocompaction my_keyspace users orders products

With Verification¶

# Enable and verify
nodetool enableautocompaction my_keyspace my_table
nodetool statusautocompaction my_keyspace my_table
# Expected: running=true

When to Use¶

After Bulk Data Loading¶

Re-enable compaction after loading large amounts of data:

# 1. Disable compaction before bulk load
nodetool disableautocompaction my_keyspace my_table

# 2. Load data (sstableloader, COPY, etc.)
sstableloader -d node1,node2 /path/to/sstables/

# 3. Re-enable compaction
nodetool enableautocompaction my_keyspace my_table

# 4. Optionally force immediate compaction
nodetool compact my_keyspace my_table

After Maintenance Operations¶

Restore normal operation after maintenance:

# After repair or other maintenance
nodetool enableautocompaction my_keyspace

# Monitor compaction activity
watch nodetool compactionstats

After Troubleshooting¶

When compaction was disabled to investigate issues:

# Issue identified and resolved
nodetool enableautocompaction

# Verify compaction resumes
nodetool compactionstats

After Node Recovery¶

When bringing a node back to normal operation:

# Node recovered, restore full functionality
nodetool enableautocompaction

# Check for compaction backlog
nodetool compactionstats

Behavior¶

What Happens When Enabled¶

The table is marked as eligible for automatic compaction
The compaction strategy begins evaluating SSTables
Compaction tasks are scheduled based on strategy rules
Pending compaction backlog begins processing

Compaction Strategy Interaction¶

The enabled auto-compaction respects the table's configured compaction strategy:

Strategy	Behavior After Enable
SizeTieredCompactionStrategy (STCS)	Compacts SSTables of similar sizes
LeveledCompactionStrategy (LCS)	Promotes SSTables through levels
TimeWindowCompactionStrategy (TWCS)	Compacts within time windows
UnifiedCompactionStrategy (UCS)	Adaptive compaction (Cassandra 5.0+)

Impact Assessment¶

Immediate Effects¶

Aspect	Impact
Compaction scheduling	Resumes immediately
Disk I/O	May increase as backlog processes
CPU usage	Compaction threads become active
Pending tasks	Begin processing

Short-term Effects¶

Aspect	Impact
SSTable count	Begins decreasing
Read latency	Improves as SSTables merge
Disk usage	May spike during compaction
Write amplification	Normal levels resume

Compaction Backlog

If auto-compaction was disabled for an extended period, there may be a significant backlog. Monitor disk space and I/O during catch-up.

Workflow: Complete Bulk Load Procedure¶

#!/bin/bash
# bulk_load_with_compaction_control.sh

KEYSPACE="my_keyspace"
TABLE="my_table"
DATA_PATH="/path/to/sstables"

echo "=== Bulk Load with Compaction Control ==="

# 1. Check current state
echo "1. Current compaction status:"
nodetool statusautocompaction $KEYSPACE $TABLE

# 2. Disable auto-compaction
echo "2. Disabling auto-compaction..."
nodetool disableautocompaction $KEYSPACE $TABLE

# 3. Verify disabled
echo "3. Verifying disabled:"
nodetool statusautocompaction $KEYSPACE $TABLE

# 4. Load data
echo "4. Loading data..."
sstableloader -d localhost $DATA_PATH

# 5. Re-enable auto-compaction
echo "5. Re-enabling auto-compaction..."
nodetool enableautocompaction $KEYSPACE $TABLE

# 6. Verify enabled
echo "6. Verifying enabled:"
nodetool statusautocompaction $KEYSPACE $TABLE

# 7. Check compaction activity
echo "7. Current compaction activity:"
nodetool compactionstats

echo "=== Complete ==="

Monitoring After Enable¶

Check Compaction Activity¶

# View active and pending compactions
nodetool compactionstats

Example output showing compaction resuming:

pending tasks: 15
- my_keyspace.my_table: 15

Active compaction remaining time :   0h00m45s
        compaction type   keyspace         table   completed      total    unit   progress
         Compaction   my_keyspace      my_table   524288000   1048576000   bytes     50.00%

Monitor Over Time¶

# Watch compaction progress
watch -n 5 'nodetool compactionstats'

Check SSTable Counts¶

# Before re-enabling (many SSTables)
nodetool tablestats my_keyspace.my_table | grep "SSTable count"
# SSTable count: 47

# After compaction catches up (fewer SSTables)
nodetool tablestats my_keyspace.my_table | grep "SSTable count"
# SSTable count: 8

Troubleshooting¶

Compaction Not Starting After Enable¶

If compaction doesn't start after enabling:

# Verify status is enabled
nodetool statusautocompaction my_keyspace my_table

# Check for pending tasks
nodetool compactionstats

# If no pending tasks, may need to wait for strategy evaluation
# Or force compaction
nodetool compact my_keyspace my_table

High I/O After Enable¶

If I/O is too high after enabling:

# Reduce compaction throughput temporarily
nodetool setcompactionthroughput 32

# Let backlog process gradually
watch nodetool compactionstats

# Restore normal throughput later
nodetool setcompactionthroughput 64

Disk Space Issues¶

If disk space is critical:

# Check current usage
df -h /var/lib/cassandra

# May need to process compaction slowly
nodetool setcompactionthroughput 16

# Clear snapshots if needed
nodetool clearsnapshot --all

Cluster-Wide Operations¶

Enable on All Nodes¶

#!/bin/bash
# enable_autocompaction_cluster.sh

KEYSPACE="my_keyspace"
TABLE="my_table"

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

for node in $nodes; do
    echo "Enabling auto-compaction on $node..."
    ssh "$node" "nodetool enableautocompaction $KEYSPACE $TABLE"
done

echo "Verification:"
for node in $nodes; do
    echo -n "$node: "
    ssh "$node" "nodetool statusautocompaction $KEYSPACE $TABLE"
done

Best Practices¶

Auto-Compaction Guidelines

Re-enable promptly - Don't leave auto-compaction disabled for extended periods
Verify after enabling - Always check with statusautocompaction
Monitor the backlog - Watch compactionstats for catch-up progress
Control throughput - Adjust compaction throughput if I/O impact is too high
Check disk space - Ensure sufficient space for compaction to proceed
Document changes - Log when and why auto-compaction was disabled/enabled
Apply consistently - Enable on all nodes if disabled cluster-wide

Long-term Disable Risks

Keeping auto-compaction disabled for extended periods causes:

SSTable proliferation (many small files)
Degraded read performance
Increased memory usage for bloom filters
Tombstone accumulation
Potential disk space issues

Command	Relationship
disableautocompaction	Disable auto-compaction
statusautocompaction	Check auto-compaction status
compact	Force manual compaction
compactionstats	View active compactions
setcompactionthroughput	Control compaction rate
tablestats	View SSTable counts