Storage Optimization

Compression Codecs

• Default: LZ4 — fast, moderate compression
• ZSTD(level) — better compression, slower. Level 1-22 (3 is good default)
• Delta + ZSTD — excellent for time-series monotonic data
• DoubleDelta — best for timestamps and counters
• Gorilla — optimized for floating-point gauge metrics
• T64 — for integer columns with small range
• Per-column: ALTER TABLE t MODIFY COLUMN col TYPE UInt32 CODEC(Delta, ZSTD(3))
• In-place codec change: ALTER TABLE t MODIFY COLUMN col CODEC(Delta, ZSTD(3))

TTL Policies

• Table-level: ALTER TABLE t MODIFY TTL event_time + INTERVAL 90 DAY
• Column-level: ALTER TABLE t MODIFY COLUMN oldcol TTL eventtime + INTERVAL 30 DAY
• Move to volume: TTL event_time + INTERVAL 7 DAY TO VOLUME 'cold'
• Delete: TTL event_time + INTERVAL 365 DAY DELETE
• Monitor TTL merges: system.merges WHERE isttlmerge = 1

Tiered Storage

• Define storage policies in config: hot (SSD) → warm (HDD) → cold (S3)
• <storage_configuration> in config.xml
• Move rules: TTL event_time + INTERVAL 7 DAY TO DISK 'hdd'
• Check disk usage: system.disks
• Check volume usage: system.storage_policies

Part Management

• Monitor part count: SELECT count() FROM system.parts WHERE active AND database = 'db' AND table = 't'
• Too many parts (>300 per partition) = degraded performance
• Detached parts: check system.detached_parts, clean with DROP DETACHED PART
• Part size target: 1-10GB per part for optimal performance

Disk Space Recovery

• DROP PARTITION for bulk deletion by time
• TRUNCATE TABLE for full table cleanup
• Check for orphaned data: detached parts, temporary files
• System tables can grow large — set TTL on querylog, tracelog, etc.
• Load the troubleshooting skill for disk-full recovery procedures.