ClickHouse DB::Exception: Not enough space

The "DB::Exception: Not enough space" error in ClickHouse occurs when the system runs out of available disk space to perform operations or store data.

Impact

This error can have significant impact on database operations:

• Inability to insert new data
• Failure of queries that require temporary disk space
• Potential data loss if the system cannot complete write operations
• Degraded performance due to limited space for temporary files and caches

Common Causes

1. Insufficient disk space allocation for ClickHouse data directory
2. Rapid data growth without proper capacity planning
3. Large temporary files from complex queries filling up disk space
4. Accumulation of old data that hasn't been properly archived or deleted
5. System logs or crash dumps consuming excessive space

Troubleshooting and Resolution Steps

1. Check available disk space:

   df -h
   

2. Identify large files or directories:

   du -h /path/to/clickhouse/data | sort -rh | head -n 20
   

3. Remove unnecessary files or move them to a different storage location.

4. Optimize tables to reclaim space:

   OPTIMIZE TABLE your_table FINAL;
   

5. Implement a data retention policy to automatically remove old data.

6. Increase disk space by adding new disks or expanding existing volumes.

7. Configure ClickHouse to use multiple disks for data storage.

8. Review and adjust settings related to max_table_size_to_drop and max_partition_size_to_drop.

Best Practices

1. Implement regular monitoring of disk usage and set up alerts for low disk space.
2. Use ClickHouse's built-in TTL (Time to Live) feature for automatic data management.
3. Regularly review and optimize your data schema and compression settings.
4. Consider using ClickHouse's distributed storage to spread data across multiple nodes.
5. Implement proper capacity planning and forecasting for data growth.

Frequently Asked Questions

Q: How can I prevent the "Not enough space" error from occurring?
A: Implement proactive monitoring, use data retention policies, optimize tables regularly, and plan for capacity growth in advance.

Q: Can ClickHouse automatically manage disk space?
A: ClickHouse can automatically manage some aspects of disk usage through TTL settings and automatic merges, but overall space management requires administrator oversight.

Q: What's the quickest way to free up space in an emergency?
A: Identify and remove unnecessary large files, drop unused tables, or move cold data to external storage temporarily.

Q: How does the "Not enough space" error affect running queries?
A: Running queries may fail, especially those requiring temporary space for sorting or joining large datasets. Inserts will also fail until space is freed.

Q: Can I configure ClickHouse to use multiple disks for storage?
A: Yes, ClickHouse supports configuring multiple disks for data storage, which can help distribute data and manage space more effectively.