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

partial_merge_join_left_table_buffer_bytes

If not 0 group left table blocks in bigger ones for left-side table in partial merge join. It uses up to 2x of specified memory per joining thread.

partial_merge_join_rows_in_right_blocks

Limits sizes of right-hand join data blocks in partial merge join algorithm for JOIN queries. ClickHouse server:
  1. Splits right-hand join data into blocks with up to the specified number of rows.
  2. Indexes each block with its minimum and maximum values.
  3. Unloads prepared blocks to disk if it is possible.
Possible values:
  • Any positive integer. Recommended range of values: [1000, 100000].
Last modified on July 23, 2026