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921518db0a
* add the query data deduplication excluding duplicated parts in MergeTree family engines. query deduplication is based on parts' UUID which should be enabled first with merge_tree setting assign_part_uuids=1 allow_experimental_query_deduplication setting is to enable part deduplication, default ot false. data part UUID is a mechanism of giving a data part a unique identifier. Having UUID and deduplication mechanism provides a potential of moving parts between shards preserving data consistency on a read path: duplicated UUIDs will cause root executor to retry query against on of the replica explicitly asking to exclude encountered duplicated fingerprints during a distributed query execution. NOTE: this implementation don't provide any knobs to lock part and hence its UUID. Any mutations/merge will update part's UUID. * add _part_uuid virtual column, allowing to use UUIDs in predicates. Signed-off-by: Aleksei Semiglazov <asemiglazov@cloudflare.com> address comments
6 lines
103 B
XML
6 lines
103 B
XML
<yandex>
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<merge_tree>
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<assign_part_uuids>1</assign_part_uuids>
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</merge_tree>
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</yandex>
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