clickhouse
https://github.com/yandex/clickhouse
C++
ClickHouse is a free analytic DBMS for big data.
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- Issues
- Do not look up a stream file for the size hints of every granule of a Compact part
- Parquet ORDER BY <String> LIMIT with s != '' skips no row groups because every minimum is ''; bounding them by their dictionary makes ClickBench Q26 12-16% faster
- Fix ZNONODE race when reading StorageKafka2 topic partition locks
- parseDateTime resets month and day when a weekday follows the date
- Parquet: decoding dictionary indexes under a PREWHERE filter re-scans the filter for every run; one bitmask per call makes ClickBench Q31 and Q12 7-10% faster
- `mapValues` `bloom_filter` throws `BAD_GET`: constant not cast to value type
- Parquet over S3 at default settings waits a full round trip for each separately read row group; reading the next one ahead makes ClickBench S3 queries 20-27% faster
- Parquet: per-value PREWHERE on a dictionary column scans and renumbers all indexes of every block to drop unused values; marking them while decoding makes ClickBench Q11 and Q12 13-16% faster
- MergeTree index analysis builds a condition for every skip index on each filtered query: skip indexes the filter does not read (ClickBench Q41 -33%, Q42 -29% with min-max indexes on all numeric and date columns)
- Report a missing file instead of an unknown table for a URL database
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