v.24.10Experimental Feature

Parallel Replicas Transition from Experimental to Beta with New Settings in ClickHouse

Official CH changelog text
Parallel replicas are moved from experimental to beta. Reworked settings that control the behavior of parallel replicas algorithms. A quick recap: ClickHouse has four different algorithms for parallel reading involving multiple replicas, which is reflected in the setting parallel_replicas_mode, the default value for it is read_tasks Additionally, the toggle-switch setting enable_parallel_replicas has been added. #63151 (Alexey Milovidov), (Nikita Mikhaylov).
Parallel replicas feature in ClickHouse has been promoted from experimental to beta status, with reworked settings controlling the behavior of parallel reading algorithms across replicas.

Why it matters

This feature improves query performance and fault tolerance by enabling parallel reading from multiple replicas using different algorithms. Moving it to beta stabilizes its usage and provides clearer control to users over how parallel reads are performed, enhancing resource utilization and query efficiency.

How to use it

Users can enable or configure parallel replicas behavior via the setting enable_parallel_replicas to toggle the feature on or off. The setting parallel_replicas_mode controls which of the four available reading algorithms is used (default is read_tasks). These settings allow users to customize parallel reading according to their workload requirements.

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