Aleksei Semiglazov 921518db0a CLICKHOUSE-606: query deduplication based on parts' UUID ...

* 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

2021-02-02 16:53:39 +00:00

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