Append-only Storage

How append-only storage works

Append-only storage treats data as an immutable log of events, where each new record is written sequentially after the previous one. This pattern aligns naturally with time-series data, where newer events occur later in time and are written in chronological order.

The sequential nature of writes eliminates the need for random disk access during ingestion, leading to significantly improved write performance.

Benefits for time-series workloads

Optimized write performance

Since data is only written to the end of files, the storage system can optimize for sequential writes, which are much faster than random writes. This is particularly important for time-series databases that handle high-volume data ingestion.

Data immutability

The append-only nature ensures that historical data remains unchanged, providing:

• Reliable audit trails
• Simplified backup and recovery
• Consistent point-in-time views of data

Efficient compaction

When combined with compaction, append-only storage enables efficient background processes to optimize data organization without impacting ongoing writes.

Implementation considerations

Write-ahead logging

Many systems implement append-only storage through a write-ahead log, which provides:

• Durability guarantees
• Crash recovery
• Transaction support

Storage management

To prevent unlimited growth, implementations typically include:

• Time-based retention policies
• Storage tiering for older data
• Background compaction processes

Here's how a typical append-only storage system handles writes:

Performance implications

Write optimization

• Sequential writes maximize disk throughput
• Reduced write amplification
• Minimized disk seek operations

Read considerations

While append-only storage optimizes writes, reading requires additional strategies:

• Index structures for efficient queries
• Partition pruning to limit scan ranges
• Caching frequently accessed data

Real-world applications

Financial market data

Append-only storage is ideal for capturing market data where:

• Historical accuracy is critical
• Write speeds are paramount
• Data must be auditable

Industrial telemetry

Sensor data collection benefits from:

• High-speed sequential writes
• Immutable historical records
• Time-based querying capabilities

Event logging

System and application logs leverage:

• Sequential write performance
• Natural time-based organization
• Simplified backup and retention

Best practices

1. Implement appropriate retention policies
2. Use efficient compression strategies
3. Balance partition sizes for optimal performance
4. Monitor storage growth and compaction metrics
5. Plan for disaster recovery scenarios

The effectiveness of append-only storage depends on careful consideration of these factors within your specific use case.