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

parts_to_delay_insert

If the number of active parts in a single partition exceeds the parts_to_delay_insert value, an INSERT is artificially slowed down. Possible values:
  • Any positive integer.
ClickHouse artificially executes INSERT longer (adds ‘sleep’) so that the background merge process can merge parts faster than they are added.

parts_to_throw_insert

If the number of active parts in a single partition exceeds the parts_to_throw_insert value, INSERT is interrupted with the Too many parts (N). Merges are processing significantly slower than inserts exception. Possible values:
  • Any positive integer.
To achieve maximum performance of SELECT queries, it is necessary to minimize the number of parts processed, see Merge Tree. Prior to version 23.6 this setting was set to 300. You can set a higher different value, it will reduce the probability of the Too many parts error, but at the same time SELECT performance might degrade. Also in case of a merge issue (for example, due to insufficient disk space) you will notice it later than you would with the original 300.
Last modified on July 23, 2026