nodetool getcompactionthroughput

Displays the current compaction throughput limit.

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Synopsis

nodetool [connection_options] getcompactionthroughput [options]

See connection options for connection options.

Options

Option	Description
-d, --precise-mib	Display precise MiB/s value as a decimal (avoids rounding errors when configured value is not an integer)

Description

nodetool getcompactionthroughput returns the maximum rate at which compaction operations can write data, measured in mebibytes per second (MiB/s). The output also includes current throughput metrics for the last 1/5/15 minute intervals. This throttle helps prevent compaction from consuming excessive disk I/O and impacting read/write performance.

Compaction throughput affects:

• SSTable merge operations - How fast SSTables are combined
• Disk I/O utilization - Balance between compaction and client traffic
• Compaction backlog - How quickly pending compactions complete
• Read performance - Fewer SSTables means faster reads

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Output

Standard Output

Current compaction throughput: 64 MiB/s
throughput_1min: 45 MiB/s
throughput_5min: 52 MiB/s
throughput_15min: 48 MiB/s

Output Values

Value	Meaning
64 MiB/s	Default throughput limit
0 MiB/s	Unlimited (no throttling)
16-256 MiB/s	Typical operational range

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Examples

Basic Usage

nodetool getcompactionthroughput

Output:

Current compaction throughput: 64 MB/s

Check Remote Node

ssh 192.168.1.100 "nodetool getcompactionthroughput"

Cluster-Wide Check

for node in node1 node2 node3; do
    echo -n "$node: "
    ssh "$node" "nodetool getcompactionthroughput"
done

Extract Value Only

nodetool getcompactionthroughput | awk '{print $4}'

Output:

64

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Understanding Compaction Throughput

How Throttling Works

Cassandra limits the rate at which compaction writes output SSTables:

1. Compaction reads input SSTables
2. Merges and processes data in memory
3. Writes output SSTables at throttled rate
4. Rate is controlled by compaction throughput setting

Impact of Different Values

Throughput	Compaction Speed	I/O Impact	Use Case
16 MB/s	Very slow	Minimal	Heavy read load
32 MB/s	Slow	Low	Normal production
64 MB/s	Moderate	Moderate	Default/balanced
128 MB/s	Fast	High	Maintenance windows
256+ MB/s	Very fast	Very high	Dedicated compaction
0 (unlimited)	Maximum	Maximum	Recovery/emergency

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When to Use

Routine Monitoring

Check current throughput setting:

nodetool getcompactionthroughput

Before Adjusting

Verify current value before making changes:

# Check current
nodetool getcompactionthroughput

# Adjust if needed
nodetool setcompactionthroughput 128

# Verify change
nodetool getcompactionthroughput

During Compaction Issues

When investigating compaction performance:

# Check throughput limit
nodetool getcompactionthroughput

# Check current compaction activity
nodetool compactionstats

# Check if throughput is the bottleneck
# (compare active rate vs configured limit)

Cluster Configuration Audit

Verify consistency across nodes:

#!/bin/bash
# Check compaction throughput on all nodes

echo "=== Compaction Throughput Audit ==="
for node in $(nodetool status | grep "^UN" | awk '{print $2}'); do
    throughput=$(ssh "$node" "nodetool getcompactionthroughput 2>/dev/null | awk '{print $4}')"
    echo "$node: $throughput MB/s"
done

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Correlation with Compaction Stats

Monitoring Actual Throughput

# Check configured limit
nodetool getcompactionthroughput

# Check actual compaction activity
nodetool compactionstats

Example compactionstats output:

pending tasks: 5
- system_schema.tables: 0
- my_keyspace.my_table: 5

Active compaction:
   Compacting (my_keyspace.my_table)
   Progress: 45.2% (2.3/5.1 GB)
   Throughput: 62.5 MB/s

If "Throughput" consistently matches the configured limit, compaction is being throttled.

Signs Throughput is Too Low

Indicator	Symptom
Growing pending tasks	nodetool compactionstats shows increasing backlog
High SSTable count	nodetool tablestats shows many SSTables
Read latency increase	More SSTables to scan for reads
Disk usage growth	Uncompacted data accumulating

Signs Throughput is Too High

Indicator	Symptom
I/O saturation	High disk utilization (iostat)
Read/write latency	Client operations slowed
Dropped messages	nodetool tpstats shows drops
CPU pressure	Compaction using too much CPU

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Default Values

Default Value

The default compaction throughput is 64 MB/s in Cassandra 4.x and later.

Configuration File

The cassandra.yaml parameter name varies by version:

Cassandra Version	Parameter Name	Example
Pre-4.1	compaction_throughput_mb_per_sec	64
4.1+	compaction_throughput	64MiB/s

# cassandra.yaml (4.1+)
compaction_throughput: 64MiB/s

# cassandra.yaml (Pre-4.1)
# compaction_throughput_mb_per_sec: 64

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Comparison with Related Settings

Setting	Purpose	Command
Compaction throughput	SSTable write rate limit	getcompactionthroughput / setcompactionthroughput
Stream throughput	Node-to-node transfer rate	getstreamthroughput / setstreamthroughput
Concurrent compactors	Parallel compaction threads	getconcurrentcompactors / setconcurrentcompactors

Understanding the Relationship

# Check all compaction-related settings
echo "=== Compaction Settings ==="
echo "Throughput: $(nodetool getcompactionthroughput)"
echo "Concurrent compactors: $(nodetool getconcurrentcompactors)"
echo ""
echo "=== Current Activity ==="
nodetool compactionstats

Effective throughput = throughput_per_compactor × concurrent_compactors

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Tuning Guidelines

When to Increase

• Compaction backlog growing
• Many pending compaction tasks
• During maintenance windows
• SSTable count too high

# Check current
nodetool getcompactionthroughput

# Increase for maintenance
nodetool setcompactionthroughput 128

# Monitor progress
watch nodetool compactionstats

When to Decrease

• High client latencies during compaction
• I/O contention observed
• Disk utilization too high
• During peak traffic periods

# Check current
nodetool getcompactionthroughput

# Reduce to minimize impact
nodetool setcompactionthroughput 32

# Verify client latencies improve
nodetool proxyhistograms

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Monitoring Script

#!/bin/bash
# compaction_monitor.sh - Monitor compaction throughput and activity

while true; do
    clear
    echo "=== Compaction Monitor $(date) ==="
    echo ""

    # Configured limit
    echo "Configured throughput: $(nodetool getcompactionthroughput)"
    echo ""

    # Current activity
    echo "Current compaction activity:"
    nodetool compactionstats

    echo ""
    echo "Press Ctrl+C to exit"
    sleep 10
done

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Troubleshooting

Throughput Shows 0

nodetool getcompactionthroughput
# Output: Current compaction throughput: 0 MB/s

This means compaction is unlimited (no throttling). This is intentional in some configurations but may cause I/O saturation.

# Set a reasonable limit
nodetool setcompactionthroughput 64

Value Doesn't Persist After Restart

Runtime changes with setcompactionthroughput don't persist. Update cassandra.yaml:

compaction_throughput_mb_per_sec: 64

Different Values Across Nodes

# Audit cluster
for node in node1 node2 node3; do
    echo "$node: $(ssh "$node" "nodetool getcompactionthroughput | awk '{print $4}')""
done

# Output:
# node1: 64
# node2: 32  # Different!
# node3: 64

# Standardize
ssh node2 "nodetool setcompactionthroughput 64"

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Best Practices

Compaction Throughput Guidelines

1. Monitor regularly - Include in operational dashboards
2. Consistent across cluster - Use same setting on all nodes
3. Adjust for workload - Lower during peak, higher during maintenance
4. Balance with streaming - Consider total I/O budget
5. Document changes - Log when and why throughput was adjusted
6. Persist settings - Update cassandra.yaml for permanent changes

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Related Commands

Command	Relationship
setcompactionthroughput	Modify throughput limit
compactionstats	View active compactions
compactionhistory	View past compactions
setstreamthroughput	Set streaming rate
tablestats	SSTable counts per table