2025 Changelog

#### Performance Improvement[​](#performance-improvement-10 "Direct link to Performance Improvement")

- Improve performance of the whole JSON column reading in Wide parts from S3. It's done by adding prefetches for subcolumn prefixes deserialization, cache of deserialized prefixes, and parallel deserialization of subcolumn prefixes. It improves the reading of the JSON column from S3 4 times in queries like `SELECT data FROM table` and about 10 times in queries like `SELECT data FROM table LIMIT 10`. [#74827](https://github.com/ClickHouse/ClickHouse/pull/74827) ([Pavel Kruglov](https://github.com/Avogar)).
- Fixed unnecessary contention in `parallel_hash` when `max_rows_in_join = max_bytes_in_join = 0`. [#75155](https://github.com/ClickHouse/ClickHouse/pull/75155) ([Nikita Taranov](https://github.com/nickitat)).
- Fixed double preallocation in `ConcurrentHashJoin` in case join sides are swapped by the optimizer. [#75149](https://github.com/ClickHouse/ClickHouse/pull/75149) ([Nikita Taranov](https://github.com/nickitat)).
- Slight improvement in some join scenarios: precalculate the number of output rows and reserve memory for them. [#75376](https://github.com/ClickHouse/ClickHouse/pull/75376) ([Alexander Gololobov](https://github.com/davenger)).
- For queries like `WHERE a < b AND b < c AND c < 5`, we can infer new comparing conditions (`a < 5 AND b < 5`) to have better filter ability. [#73164](https://github.com/ClickHouse/ClickHouse/pull/73164) ([Shichao Jin](https://github.com/jsc0218)).
- Keeper improvement: disable digest calculation when committing to in-memory storage for better performance. It can be enabled with `keeper_server.digest_enabled_on_commit` config. Digest is still calculated when preprocessing requests. [#75490](https://github.com/ClickHouse/ClickHouse/pull/75490) ([Antonio Andelic](https://github.com/antonio2368)).
- Push down filter expression from JOIN ON when possible. [#75536](https://github.com/ClickHouse/ClickHouse/pull/75536) ([Vladimir Cherkasov](https://github.com/vdimir)).
- Calculate columns and indices sizes lazily in MergeTree. [#75938](https://github.com/ClickHouse/ClickHouse/pull/75938) ([Pavel Kruglov](https://github.com/Avogar)).
- Reintroduce respect `ttl_only_drop_parts` on `MATERIALIZE TTL`; only read necessary columns to recalculate TTL and drop parts by replacing them with an empty ones. [#72751](https://github.com/ClickHouse/ClickHouse/pull/72751) ([Andrey Zvonov](https://github.com/zvonand)).
- Reduce write buffer size for plain\_rewritable metadata files [#75758](https://github.com/ClickHouse/ClickHouse/pull/75758) ([Julia Kartseva](https://github.com/jkartseva)).
- Reduce memory usage for some window functions. [#65647](https://github.com/ClickHouse/ClickHouse/pull/65647) ([lgbo](https://github.com/lgbo-ustc)).
- Evaluate parquet bloom filters and min/max indexes together. Necessary to properly support: `x = 3 or x > 5` where data = [1, 2, 4, 5]. [#71383](https://github.com/ClickHouse/ClickHouse/pull/71383) ([Arthur Passos](https://github.com/arthurpassos)).
- Queries passed to the `Executable` storage are no longer limited to a single-threaded execution. [#70084](https://github.com/ClickHouse/ClickHouse/pull/70084) ([yawnt](https://github.com/yawnt)).
- Fetch parts in parallel in ALTER TABLE FETCH PARTITION (thread pool size is controlled with `max_fetch_partition_thread_pool_size`). [#74978](https://github.com/ClickHouse/ClickHouse/pull/74978) ([Azat Khuzhin](https://github.com/azat)).
- Allow to move predicates with the `indexHint` function to `PREWHERE`. [#74987](https://github.com/ClickHouse/ClickHouse/pull/74987) ([Anton Popov](https://github.com/CurtizJ)).

#### Improvement[​](#improvement-10 "Direct link to Improvement")