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

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primary_key_compress_block_size

Size, in uncompressed bytes, of blocks used when writing a compressed primary-key index for new or rewritten data parts. Applies only when compress_primary_key is enabled. This controls compression framing and buffering; it does not change the primary key or index granularity.

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primary_key_compression_codec

Compression encoding used by primary, primary key is small enough and cached, so the default compression is ZSTD(3).

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primary_key_lazy_load

Load primary key in memory on first use instead of on table initialization. This can save memory in the presence of a large number of tables.

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primary_key_ratio_of_unique_prefix_values_to_skip_suffix_columns

If the value of a column of the primary key in data part changes at least in this ratio of times, skip loading next columns in memory. This allows to save memory usage by not loading useless columns of the primary key.
Last modified on October 4, 2026