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

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enable_parallel_blocks_marshalling

Affects only distributed queries. If enabled, blocks will be (de)serialized and (de)compressed on pipeline threads (i.e. with higher parallelism that what we have by default) before/after sending to the initiator.

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enable_parallel_single_level_merge

Parallelize the final merge of the per-thread single-level aggregation hash tables. The key space is split into disjoint partitions by key hash, and each partition is merged independently: the merging thread enumerates all per-thread tables and combines the keys that belong to its partition, so no two threads ever touch the same key. If the setting is turned off, the single-level tables are merged serially on one thread. Aggregation by 8- and 16-bit keys keeps its own range-partitioned parallel merge regardless of this setting.
Last modified on August 3, 2026