---
title: "ClickHouse Release 26.3"
description: "ClickHouse 26.3 delivers twenty-seven new features, forty performance optimizations, and over two hundred bug fixes. Common table expressions can now be materialized into temporary tables via the MATERIALIZED clause when enabled, evaluating subqueries once to reduce query execution times and peak memory usage. The query optimizer expands join reordering beyond inner and left or right joins to include anti, semi, and full joins when table statistics are available. In addition, user-defined functions can run compiled WebAssembly code inside sandboxed Wasmtime runtimes. Storage for the Map data type also introduces hash-based bucketing during background merges, accelerating single-key lookups by two to forty-nine times without slowing initial inserts."
---

# ClickHouse Release 26.3

[Clickhouse](https://yomu.fyi/company/clickhouse) · ClickHouse · Apr 7, 2026

**Type:** Announcement

## Summary

ClickHouse 26.3 delivers twenty-seven new features, forty performance optimizations, and over two hundred bug fixes. Common table expressions can now be materialized into temporary tables via the MATERIALIZED clause when enabled, evaluating subqueries once to reduce query execution times and peak memory usage. The query optimizer expands join reordering beyond inner and left or right joins to include anti, semi, and full joins when table statistics are available. In addition, user-defined functions can run compiled WebAssembly code inside sandboxed Wasmtime runtimes. Storage for the Map data type also introduces hash-based bucketing during background merges, accelerating single-key lookups by two to forty-nine times without slowing initial inserts.

## Context

ClickHouse workloads faced inefficiencies such as full array scans during Map lookups, repeated evaluation of identical subqueries in CTEs, and join reordering limitations restricted only to inner and left or right joins.

## Approach / What changed

ClickHouse 26.3 introduces materialized CTEs stored in temporary tables, bucketed Map data serialization applied during background merges, join reordering across ANTI, SEMI, and FULL joins, and experimental WebAssembly UDF execution.

## Takeaways

- Setting enable\_materialized\_cte to 1 enables the MATERIALIZED keyword in CTEs to evaluate subqueries only once into temporary tables, lowering memory consumption and query times.
- Join reordering now covers ANTI, SEMI, and FULL joins when table statistics are enabled, allowing the optimizer to automatically pick the most efficient build side.
- Configuring map\_serialization\_version to with\_buckets splits Map keys into hash-based buckets during background merges, accelerating single-key lookups by 2x to 49x.

**Tags:** [Observability](https://yomu.fyi/topic/observability), [Open Source](https://yomu.fyi/topic/open-source), [Performance](https://yomu.fyi/topic/performance)

- Source: [Clickhouse](https://clickhouse.com/blog/clickhouse-release-26-03)
- Source URL: https://clickhouse.com/blog/clickhouse-release-26-03
- Ingested by Yomu: 2026-08-28T01:23:48.628Z

[Read original post](https://clickhouse.com/blog/clickhouse-release-26-03)