clickhouse
https://github.com/yandex/clickhouse
C++
ClickHouse is a free analytic DBMS for big data.
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- Issues
- PREWHERE Map subcolumn costing performs full-table metadata I/O before pruning
- AST fuzzer: do not create a view that duplicates a non-parallel sink
- Add is_nullable to system.columns, use it in information_schema
- Fix a renamed and dropped column being read from the wrong file while the mutation is pending
- Add `jsonPathValues` tokenizer for JSON text indexes
- Row policy over a file-backed table breaks `DEFAULT` columns missing from the data file (`UNKNOWN_IDENTIFIER`; silently wrong results on 26.7)
- Backport #112573 to 26.5: Fix async bounded read buffer readbigat race
- Trivial GROUP BY LIMIT optimization: support aggregate functions in the projection (2x on ClickBench Q17)
- Aggregation: precompute hashes and prefetch for preallocated hash-table variants (up to 1.5x on multi-key GROUP BY)
- Push dynamic TopN thresholds into MergeTree reads for ORDER BY ... LIMIT (2-3x on ClickBench Q24/Q26)
- Docs
- C++ not yet supported