nodetool compactionhistory

Displays the history of completed compaction operations.

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Synopsis

nodetool [connection_options] compactionhistory

See connection options for connection options.

Description

nodetool compactionhistory shows information about previously completed compactions. This helps analyze compaction patterns, identify problematic tables, and understand historical compaction behavior.

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Output Format

Compaction History:
id                                   keyspace_name columnfamily_name compacted_at            bytes_in    bytes_out   rows_merged     compaction_properties
abc12345-def6-7890-abcd-ef1234567890 my_keyspace   my_table          2024-01-15T10:30:00     1073741824  536870912   {1:150, 2:50}   {id:abc12345-...}
def67890-abcd-1234-ef56-7890abcdef12 my_keyspace   my_table          2024-01-15T09:15:00     2147483648  1073741824  {1:300, 2:100}  {id:def67890-...}

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Output Fields

Field	Description
id	Unique compaction ID
keyspace_name	Keyspace containing the table
columnfamily_name	Table name
compacted_at	Timestamp of compaction completion
bytes_in	Total bytes read from input SSTables
bytes_out	Total bytes written to output SSTable
rows_merged	Distribution of rows merged per SSTable
compaction_properties	Additional compaction metadata (strategy-specific properties)

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Examples

View All Compaction History

nodetool compactionhistory

Filter by Keyspace

nodetool compactionhistory | grep my_keyspace

Filter by Table

nodetool compactionhistory | grep my_table

Recent Compactions Only

nodetool compactionhistory | head -20

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Understanding the Output

Bytes In vs Bytes Out

bytes_in: 1073741824  bytes_out: 536870912

• bytes_in > bytes_out: Data was compacted (tombstones removed, duplicates merged)
• bytes_in ≈ bytes_out: Little compaction benefit (fresh data)
• High ratio indicates effective compaction

Rows Merged

rows_merged: {1:150, 2:50}

• 1:150 - 150 rows appeared in only 1 SSTable (no merging needed)
• 2:50 - 50 rows appeared in 2 SSTables (were merged)

Higher numbers in the merge count indicate more overwrites or deletions being resolved.

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Analysis Use Cases

Check Compaction Efficiency

# Calculate compression ratio for recent compactions
nodetool compactionhistory | awk 'NR>2 {
    if ($5 > 0) {
        ratio = $6 / $5
        printf "%s.%s: %.2f\n", $2, $3, ratio
    }
}' | head -10

Ratio close to 1.0 = little benefit; lower ratio = good compaction.

Find Tables with Most Compactions

nodetool compactionhistory | awk 'NR>2 {print $2"."$3}' | sort | uniq -c | sort -rn | head -10

Check Compaction Timestamps

# See when compactions occurred
nodetool compactionhistory | awk 'NR>2 {print $4}' | cut -dT -f1 | sort | uniq -c

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Troubleshooting with Compaction History

Frequent Small Compactions

If seeing many small compactions:

nodetool compactionhistory | awk 'NR>2 && $5 < 100000000 {print}' | wc -l

Many small compactions may indicate:

• High write rate
• STCS with small sstable_size_in_mb
• Need to tune compaction settings

Large Compactions Taking Too Long

# Find largest compactions
nodetool compactionhistory | awk 'NR>2 {print $5, $2"."$3}' | sort -rn | head -5

Consider:

• LCS for more predictable compaction sizes
• Increasing compaction throughput
• Adding more compaction threads

No Recent Compactions

If compactionhistory shows old entries only:

# Check if compactions are running
nodetool compactionstats

# Check if auto-compaction is enabled
nodetool statusautocompaction my_keyspace my_table

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Monitoring Compaction Patterns

Daily Compaction Volume

compaction_daily_stats.sh

#!/bin/bash
echo "Date,Compactions,BytesIn,BytesOut"
nodetool compactionhistory | awk 'NR>2 {
    date = substr($4, 1, 10)
    counts[date]++
    bytes_in[date] += $5
    bytes_out[date] += $6
}
END {
    for (d in counts) {
        printf "%s,%d,%.2fGB,%.2fGB\n", d, counts[d], bytes_in[d]/1073741824, bytes_out[d]/1073741824
    }
}' | sort

Table-Level Analysis

#!/bin/bash
# Analyze compaction efficiency by table

echo "Table,Compactions,AvgRatio"
nodetool compactionhistory | awk 'NR>2 && $5 > 0 {
    table = $2"."$3
    counts[table]++
    ratios[table] += $6/$5
}
END {
    for (t in counts) {
        printf "%s,%d,%.3f\n", t, counts[t], ratios[t]/counts[t]
    }
}' | sort -t, -k2 -rn

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History Retention

Compaction history is stored in system.compaction_history table:

SELECT * FROM system.compaction_history LIMIT 10;

History Retention (7 Days Default)

• The system.compaction_history table has a default TTL of 7 days
• Entries are automatically removed after this retention period via TTL expiration, not compaction
• For long-term analysis, export to external monitoring before entries expire

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Related Commands

Command	Relationship
compactionstats	Current compaction status
tablestats	Table statistics including SSTable count
compact	Force compaction
setcompactionthroughput	Control compaction speed