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These settings are available in system.merge_tree_settings and are autogenerated from ClickHouse source.

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max_merge_delayed_streams_for_parallel_write

The maximum number of streams (columns) that can be flushed in parallel (analog of max_insert_delayed_streams_for_parallel_write for merges). Works only for Vertical merges.

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max_merge_selecting_sleep_ms

Maximum time to wait before trying to select parts to merge again after no parts were selected. A lower setting will trigger selecting tasks in background_schedule_pool frequently which result in large amount of requests to zookeeper in large-scale clusters
Last modified on July 23, 2026