clickhouse
https://github.com/yandex/clickhouse
C++
ClickHouse is a free analytic DBMS for big data.
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- Issues
- Fix flaky 05227_system_tables_filter_by_in: hold the replication queue of t_rep
- Measure libc++ `EXTENSIVE` hardening in release builds
- Use the primary key and partition pruning for a `FixedString` key compared with a wider `FixedString`
- Do not hash `LowCardinality` dictionaries of single blocks in `DISTINCT`
- Don't keep the name of a backup entry twice
- ORDER BY count() DESC LIMIT n over a multi-key GROUP BY: aggregate only the rows of frequent key values (ClickBench Q16 -46%)
- Always report total rows to read for parallel replicas without a local plan
- GROUP BY with only count(): skip rows that repeat the previous key in the adaptive aggregator's frozen loop (ClickBench Q15 −7.5%, Q35 −6.3% on 4-core Graviton3)
- Fix duplicates in StorageKafka2: consume exactly the intent size on batch replay
- Stop re-hashing LowCardinality dictionaries in GROUP BY and in one-byte function results (high-cardinality LowCardinality GROUP BY and filters 5-9% faster)
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