clickhouse
https://github.com/yandex/clickhouse
C++
ClickHouse is a free analytic DBMS for big data.
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- Issues
- A self-join that only needs the keys holding more than one distinct value materialises every pair: one grouped pass is 65% faster on TPC-DS query 95
- Assert that a DataPartsAnyLock is constructed from a held parts lock
- GROUP BY with a nullable fixed-width key packs the key per row: packing once per block is 11% faster on TPC-DS query_65
- Look through lossless conversions of the indexed column and of constants in the text index
- Fix a TSan report on `randomnessPid` in the vendored SQLite
- A view referenced more than once in one query is read once per reference: sharing one read is 48% faster on TPC-H query 15
- Add function mapContainsKeyValue and answer it from the keyValuePairs text index
- Accept only time zone names that the built-in database has
- The set for an IN subquery is built once per query scope, so a CTE used by several UNION branches runs once per branch: TPC-DS query_23 -43%, query_14 -42%
- A correlated scalar min/max subquery reads its table a second time: computing it as a window aggregate over the rows already read is 39% faster on a TPC-H Q17-shaped query
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- C++ not yet supported