Quantrail Data

The ClickHouse 25.6 release brings a substantial set of new features, performance improvements, and bug fixes. It introduces new data types, enhances time-series capabilities, expands integration support, and delivers multiple enhancements across the storage, query engine, and developer experience. This post highlights the most relevant changes for engineering and data teams.

Key Features

• New Time Types: Time and Time64 data types enable precise time-only value storage and comparison.
• CoalescingMergeTree Engine: Automatically retains the first non-null value during merges, ideal for sparse or partially updated datasets.
• Time-Series Functions: New built-in functions (delta, rate, etc.) simplify Prometheus-style analysis.
• New Monitoring Tool: chdig, a TUI-based CLI for monitoring queries, merges, and system stats.
• WKB & MultiPolygon Support: Enhanced spatial functions for broader GIS compatibility.
• Parquet + JSON Support: Native read/write for JSON columns in Parquet files.

Performance Improvements

• Faster Inserts and Merges: Improved memory efficiency and parallelism for inserts and background merges.
• Enhanced Indexing: Better performance for Bloom filters and primary key range scans.
• Filesystem Cache: Switched to segmented LRU for smarter cache behavior.
• Improved GROUP BY: Better memory reuse in hash tables improves aggregation speed.

SQL & Engine Enhancements

• Support for USE DATABASE syntax and persistent UDFs in clickhouse-local.
• Improved Map and Array functions, and more robust JOIN and window function handling.
• Support for disk-level filtering using _disk_name.

Observability & Debugging

• New system.codecs table and improved EXPLAIN output.
• More detailed metrics for memory, disk health, and asynchronous inserts.
• system.iceberg_history table enhancements for version tracking.

Experimental & Integration Updates

• Kafka2 engine introduces partition rebalancing across replicas.
• DeltaLake and Iceberg support improvements.
• Support for querying local Delta tables via deltaLakeLocal.

Incompatible Change

• countMatches() no longer stops at empty matches by default. Use count_matches_stop_at_empty_match = 1 to restore previous behavior.

Dependency & Security Updates

Includes updates to OpenSSL, libxml2, grpc, mongo-c-driver, and other core dependencies for improved security and compatibility.

Conclusion

ClickHouse 25.6 is a strong release with focused improvements for time-series workloads, performance-critical environments, and modern data lake integration. Teams are encouraged to upgrade to benefit from the improved functionality, observability, and reliability.

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At Quantrail, we offer a fully managed ClickHouse service, seamless migration assistance, and dedicated service contracts to help businesses optimize their analytics stack. Whether you need a hassle-free ClickHouse deployment, expert support, or help transitioning from another database, we’ve got you covered. Let’s talk about how we can accelerate your analytics!

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References

ClickHouse release v25.6, 2025-06-26

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