clickhouse
https://github.com/yandex/clickhouse
C++
ClickHouse is a free analytic DBMS for big data.
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- Issues
- Nullable scalar placeholder now 0: `DELETE`/`CREATE VIEW` dividing by it throw
- Wide-part `MATERIALIZE PROJECTION` freezes an unstored column's DEFAULT
- RENAME x TO y, ADD COLUMN x reads stale old x until rename mutation applies
- CD-A/CD-C gate null-rejection on outer `join_use_nulls`, not the subquery's
- Resolve a stale marker and a NaN at the same timestamp independently of order
- tokenbf_v1/ngrambf_v1 indexes hash every repeated token of a granule again; skipping tokens already added cuts INSERT by 31-46% and merges by 45%
- Text index: LIKE dictionary-scan limit abandons the scan in aggregations that read every row; skipping it there makes count() 42-63% faster
- JSON text indexes: JSONAllPaths/JSONAllValues look up every path by name per row and every value's serialization by type name; resolving both once per block makes INSERT 10-23% faster
- Skip indexes over mapKeys(m)/mapValues(m) are built from the whole Map; building text and bloom_filter indexes from the keys/values subcolumn cuts MATERIALIZE INDEX 8-64% and INSERT 6-9% (14% on the OpenTelemetry logs schema)
- Concurrent lightweight DELETE can mark an earlier mutation done without applying it
- Docs
- C++ not yet supported