nodetool compactionhistory¶

Displays the history of completed compaction operations.

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.

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-...}

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)

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

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.

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

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

Monitoring Compaction Patterns¶

Daily Compaction Volume¶

#!/bin/bash
# compaction_daily_stats.sh

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

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

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