Kanishga Subramani

Posted on Jun 26

ClickHouse 26.6 latest update

#clickhouse #database #dataengineering #devops

ClickHouse 26.6 Deep Dive: Streaming Queries, MPP Execution, Geospatial Analytics, and Developer Productivity

ClickHouse 26.6 is one of the most technically significant releases in recent months. Instead of introducing another collection of SQL functions or storage engine improvements, this release focuses on expanding the database's execution engine, improving developer productivity, and enabling new classes of analytical workloads.

The release introduces continuous streaming queries, multi-stage distributed execution, geospatial enhancements, query planning improvements, and several features that simplify database optimization and observability.

Let's examine the most important changes from an engineering perspective.

Streaming Queries: Moving Beyond Batch Analytics

Historically, ClickHouse has been optimized for analytical queries executed against static snapshots of data. Applications requiring near real-time updates typically resorted to polling MergeTree tables every few seconds.

ClickHouse 26.6 introduces continuous streaming queries, allowing clients to execute long-running SELECT STREAM operations over MergeTree tables.

Instead of repeatedly executing:

SELECT *
FROM events
WHERE timestamp > now() - INTERVAL 5 SECOND;

applications can maintain a persistent query that continuously emits newly inserted rows.

This significantly reduces query overhead while lowering end-to-end latency.

Typical use cases include:

Log aggregation
Fraud detection
Operational monitoring
IoT telemetry
Live dashboards
Event-driven applications

Rather than treating ClickHouse purely as an OLAP warehouse, streaming queries push it closer toward becoming a real-time analytical processing engine.

Multi-Stage Distributed Execution

Distributed query execution receives one of its largest architectural improvements in recent releases.

Previous distributed execution generally relied on worker nodes processing local data before sending intermediate results back to a coordinating server.

ClickHouse 26.6 introduces multi-stage distributed execution, enabling worker nodes to exchange intermediate datasets before producing the final result.

Conceptually, execution now resembles modern Massively Parallel Processing (MPP) databases.

Instead of:

Workers
      ↓
 Coordinator
      ↓
 Result

execution becomes:

Workers
   ↓
 Exchange
   ↓
 Workers
   ↓
 Coordinator

This scatter-gather execution model reduces bottlenecks for operations such as:

Large JOINs
GROUP BY
Distributed aggregations
Complex analytical pipelines

The primary benefits include:

Better CPU utilization
Improved cluster scalability
Reduced coordinator bottlenecks
Lower network overhead
Faster execution for wide analytical queries

For organizations operating multi-node ClickHouse clusters, this represents one of the most impactful performance improvements in the release.

Geospatial Analytics Becomes More Complete

ClickHouse has supported spatial functions for several releases, but 26.6 significantly expands geospatial capabilities.

The release introduces support for:

GeoJSON
Mapbox Vector Tiles (MVT)

GeoJSON has become the de facto standard for exchanging geographic datasets across mapping frameworks.

Native support means data can now be imported directly into ClickHouse without requiring intermediate conversion pipelines.

Similarly, Mapbox Vector Tile generation enables ClickHouse to serve tiled geographic datasets directly from SQL.

This allows developers to build complete geospatial pipelines entirely inside the database.

Example workloads include:

Fleet tracking
Delivery optimization
Ride-sharing analytics
Telecom coverage analysis
Asset monitoring
Interactive mapping applications

Rather than exporting analytical results into GIS systems, organizations can increasingly perform storage, processing, aggregation, and visualization preparation directly inside ClickHouse.

EXPLAIN WHATIF: Predictive Query Optimization

Performance tuning traditionally requires experimentation.

Database engineers often create skip indexes, benchmark workloads, and remove indexes if they fail to improve performance.

ClickHouse 26.6 introduces EXPLAIN WHATIF, allowing hypothetical skip indexes to be evaluated before they are physically created.

Instead of building an index first, the optimizer estimates its effectiveness by calculating the expected skip ratio.

For example:

EXPLAIN WHATIF
SELECT *
FROM events
WHERE user_id = 12345;

The optimizer can indicate whether a proposed skip index would eliminate a significant portion of data scans.

Benefits include:

Faster performance tuning
Reduced storage overhead
Better index selection
Lower maintenance costs

For production environments managing petabytes of data, avoiding unnecessary indexes can translate into meaningful savings.

Queryable Documentation

A surprisingly useful addition is the new system.documentation table.

Documentation is now accessible directly through SQL.

Instead of switching between the browser and terminal, developers can execute queries against the documentation itself.

This enables workflows such as:

SELECT *
FROM system.documentation
WHERE name LIKE '%JSON%';

For engineers working interactively inside ClickHouse clients, this greatly improves productivity.

It also enables IDE integrations and internal tooling built entirely on SQL.

Better Developer Experience

Although less visible than streaming or distributed execution, several usability improvements are included throughout the release.

These improvements focus on:

Better SQL diagnostics
Improved execution planning
More informative query analysis
Easier performance troubleshooting
Cleaner optimizer behavior

Collectively, these changes reduce the time required to understand query execution and diagnose performance problems.

Performance Improvements Across the Engine

Like every ClickHouse release, version 26.6 contains numerous internal optimizations.

These include improvements to:

Query planning
Memory management
Distributed execution
Parallel processing
Network communication
Execution scheduling

Many of these changes require no application modifications.

Users upgrading existing deployments automatically benefit from lower latency and improved resource utilization.

Why This Release Matters

Rather than adding isolated features, ClickHouse 26.6 strengthens several core architectural areas.

Streaming queries extend ClickHouse beyond traditional OLAP workloads into continuous analytics.

Multi-stage distributed execution improves scalability for increasingly large clusters.

Geospatial enhancements reduce reliance on external GIS systems.

EXPLAIN WHATIF makes query optimization more predictable and data-driven.

Queryable documentation lowers the barrier for developers learning new functionality while improving day-to-day productivity.

Together, these changes demonstrate ClickHouse's continued evolution from a high-performance analytical database into a comprehensive platform for real-time, distributed analytics.

Final Thoughts

ClickHouse 26.6 focuses less on incremental SQL features and more on improving the underlying architecture that powers modern analytical applications.

Continuous streaming, MPP-style execution, enhanced geospatial processing, predictive optimization, and improved observability collectively make ClickHouse better suited for petabyte-scale, low-latency analytics.

For engineering teams already running distributed ClickHouse clusters, the release offers meaningful improvements in scalability, operational efficiency, and developer experience. While many optimizations occur under the hood, they directly impact how efficiently analytical workloads execute in production, making 26.6 a compelling upgrade for organizations building modern data platforms.

DEV Community