clickhouse
https://github.com/yandex/clickhouse
C++
ClickHouse is a free analytic DBMS for big data.
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- Issues
- Move SYSTEM query commands from InterpreterSystemQuery into SystemCommandFactory
- Count statement, dictionary, window function and system log docs in the feature_docs hook
- Iceberg: TRUNCATE TABLE on Iceberg tables
- max_bytes_before_external_join converts the hash join to grace hash join at half the configured value
- Switching a ConcurrentHashJoin to GraceHashJoin mid-build serializes the slot conversion on one mutex: 15-20x slower while spilling only 1.2 GiB
- IN (subquery) with a huge set: primary key analysis sorts the whole set single-threaded, once per KeyCondition, doubling memory and dominating the query (28 s vs 1 s for the JOIN)
- `transform` and `CASE x WHEN` hash every row with SipHash when the expression is `Nullable`
- WIP DO NOT REVIEW add bazel build configuration
- Hive partitioning returns percent-encoded partition values undecoded and `__HIVE_DEFAULT_PARTITION__` as a string instead of NULL
- With `apply_patches_on_merge = 0`, TTL / DEDUPLICATE / CLEANUP merges evaluate rows without their lightweight `UPDATE` patches and delete rows the update kept
- Docs
- C++ not yet supported