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

max_avg_part_size_for_too_many_parts

The ‘too many parts’ check according to ‘parts_to_delay_insert’ and ‘parts_to_throw_insert’ will be active only if the average part size (in the relevant partition) is not larger than the specified threshold. If it is larger than the specified threshold, the INSERTs will be neither delayed or rejected. This allows to have hundreds of terabytes in a single table on a single server if the parts are successfully merged to larger parts. This does not affect the thresholds on inactive parts or total parts.

max_buckets_in_map

The maximum number of buckets for Map serialization. Works with with_buckets Map serialization. The actual number of buckets is determined by map_buckets_strategy. The maximum allowed value is 256.

max_cleanup_delay_period

Maximum period to clean old queue logs, blocks hashes and parts.

max_compress_block_size

The maximum size of blocks of uncompressed data before compressing for writing to a table. You can also specify this setting in the global settings (see max_compress_block_size setting). The value specified when the table is created overrides the global value for this setting.

max_concurrent_queries

Max number of concurrently executed queries related to the MergeTree table. Queries will still be limited by other max_concurrent_queries settings. Possible values:
  • Positive integer.
  • 0 — No limit.
Default value: 0 (no limit). Example

max_digestion_size_per_segment

Obsolete setting, does nothing.

max_file_name_length

The maximal length of the file name to keep it as is without hashing. Takes effect only if setting replace_long_file_name_to_hash is enabled. The value of this setting does not include the length of file extension. So, it is recommended to set it below the maximum filename length (usually 255 bytes) with some gap to avoid filesystem errors.

max_partitions_to_read

Limits the maximum number of partitions that can be accessed in one query. The setting value specified when the table is created can be overridden via query-level setting. Possible values:
  • Any positive integer.
You can also specify a query complexity setting max_partitions_to_read at a query / session / profile level.

max_projections

The maximum number of merge tree projections.

max_uncompressed_bytes_in_patches

The maximum uncompressed size of data in all patch parts in bytes. If amount of data in all patch parts exceeds this value, lightweight updates will be rejected. 0 - unlimited.
Last modified on July 23, 2026