2025 Changelog

#### New Feature[​](#new-feature-8 "Direct link to New Feature")

- Added CPU slot scheduling for workloads, see [the docs](https://clickhouse.com/docs/operations/workload-scheduling#cpu_scheduling) for details. [#77595](https://github.com/ClickHouse/ClickHouse/pull/77595) ([Sergei Trifonov](https://github.com/serxa)).
- `clickhouse-local` will retain its databases after restart if you specify the `--path` command line argument. This closes [#50647](https://github.com/ClickHouse/ClickHouse/issues/50647). This closes [#49947](https://github.com/ClickHouse/ClickHouse/issues/49947). [#71722](https://github.com/ClickHouse/ClickHouse/pull/71722) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Reject queries when the server is overloaded. The decision is made based on the ratio of wait time (`OSCPUWaitMicroseconds`) to busy time (`OSCPUVirtualTimeMicroseconds`). The query is dropped with some probability, when this ratio is between `min_os_cpu_wait_time_ratio_to_throw` and `max_os_cpu_wait_time_ratio_to_throw` (those are query level settings). [#63206](https://github.com/ClickHouse/ClickHouse/pull/63206) ([Alexey Katsman](https://github.com/alexkats)).
- Time travel in `Iceberg`: add setting to query `Iceberg` tables as of a specific timestamp. [#71072](https://github.com/ClickHouse/ClickHouse/pull/71072) ([Brett Hoerner](https://github.com/bretthoerner)). [#77439](https://github.com/ClickHouse/ClickHouse/pull/77439) ([Daniil Ivanik](https://github.com/divanik)).
- An in-memory cache for `Iceberg` metadata, which stores manifest files/list and `metadata.json` to speed up queries. [#77156](https://github.com/ClickHouse/ClickHouse/pull/77156) ([Han Fei](https://github.com/hanfei1991)).
- Support `DeltaLake` table engine for Azure Blob Storage. Fixes [#68043](https://github.com/ClickHouse/ClickHouse/issues/68043). [#74541](https://github.com/ClickHouse/ClickHouse/pull/74541) ([Smita Kulkarni](https://github.com/SmitaRKulkarni)).
- Added an in-memory cache for deserialized vector similarity indexes. This should make repeated approximate nearest neighbor (ANN) search queries faster. The size of the new cache is controlled by server settings `vector_similarity_index_cache_size` and `vector_similarity_index_cache_max_entries`. This feature supersedes the skipping index cache feature of earlier releases. [#77905](https://github.com/ClickHouse/ClickHouse/pull/77905) ([Shankar Iyer](https://github.com/shankar-iyer)).
- Support partition pruning in DeltaLake. [#78486](https://github.com/ClickHouse/ClickHouse/pull/78486) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Support for a background refresh in readonly `MergeTree` tables which allows querying updateable tables with an infinite amount of distributed readers (ClickHouse-native data lake). [#76467](https://github.com/ClickHouse/ClickHouse/pull/76467) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Support using custom disks to store databases metadata files. Currently it can be configured only on a global server level. [#77365](https://github.com/ClickHouse/ClickHouse/pull/77365) ([Tuan Pham Anh](https://github.com/tuanpach)).
- Support ALTER TABLE ... ATTACH|DETACH|MOVE|REPLACE PARTITION for the plain\_rewritable disk. [#77406](https://github.com/ClickHouse/ClickHouse/pull/77406) ([Julia Kartseva](https://github.com/jkartseva)).
- Add table settings for `SASL` configuration and credentials to the `Kafka` table engine. This allows configuring SASL-based authentication to Kafka and Kafka-compatible systems directly in the CREATE TABLE statement rather than having to use configuration files or named collections. [#78810](https://github.com/ClickHouse/ClickHouse/pull/78810) ([Christoph Wurm](https://github.com/cwurm)).
- Allow setting `default_compression_codec` for MergeTree tables: it is used when the CREATE query does not explicitly define one for the given columns. This closes [#42005](https://github.com/ClickHouse/ClickHouse/issues/42005). [#66394](https://github.com/ClickHouse/ClickHouse/pull/66394) ([gvoelfin](https://github.com/gvoelfin)).
- Add `bind_host` setting in the clusters configuration so that ClickHouse can use a specific network for distributed connections. [#74741](https://github.com/ClickHouse/ClickHouse/pull/74741) ([Todd Yocum](https://github.com/toddyocum)).
- Introduce a new column, `parametrized_view_parameters` in `system.tables`. Closes <https://github.com/clickhouse/clickhouse/issues/66756>. [#75112](https://github.com/ClickHouse/ClickHouse/pull/75112) ([NamNguyenHoai](https://github.com/NamHoaiNguyen)).
- Allow changing a database comment. Closes [#73351](https://github.com/ClickHouse/ClickHouse/issues/73351) ### Documentation entry for user-facing changes. [#75622](https://github.com/ClickHouse/ClickHouse/pull/75622) ([NamNguyenHoai](https://github.com/NamHoaiNguyen)).
- Support `SCRAM-SHA-256` authentication in the PostgreSQL compatibility protocol. [#76839](https://github.com/ClickHouse/ClickHouse/pull/76839) ([scanhex12](https://github.com/scanhex12)).
- Add functions `arrayLevenshteinDistance`, `arrayLevenshteinDistanceWeighted`, and `arraySimilarity`. [#77187](https://github.com/ClickHouse/ClickHouse/pull/77187) ([Mikhail f. Shiryaev](https://github.com/Felixoid)).
- The setting `parallel_distributed_insert_select` makes effect for `INSERT SELECT` into `ReplicatedMergeTree` (previously it required Distribued tables). [#78041](https://github.com/ClickHouse/ClickHouse/pull/78041) ([Igor Nikonov](https://github.com/devcrafter)).
- Introduce `toInterval` function. This function accepts 2 arguments (value and unit), and converts the value to a specific `Interval` type. [#78723](https://github.com/ClickHouse/ClickHouse/pull/78723) ([Andrew Davis](https://github.com/pulpdrew)).
- Add several convenient ways to resolve root `metadata.json` file in an iceberg table function and engine. Closes [#78455](https://github.com/ClickHouse/ClickHouse/issues/78455). [#78475](https://github.com/ClickHouse/ClickHouse/pull/78475) ([Daniil Ivanik](https://github.com/divanik)).
- Support password based auth in SSH protocol in ClickHouse. [#78586](https://github.com/ClickHouse/ClickHouse/pull/78586) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).

#### Experimental Feature[​](#experimental-feature-8 "Direct link to Experimental Feature")

- Support correlated subqueries as an argument of `EXISTS` expression in the `WHERE` clause. Closes [#72459](https://github.com/ClickHouse/ClickHouse/issues/72459). [#76078](https://github.com/ClickHouse/ClickHouse/pull/76078) ([Dmitry Novik](https://github.com/novikd)).
- Functions `sparseGrams` and `sparseGramsHashes` with ASCII and UTF8 versions added. Author: [scanhex12](https://github.com/scanhex12). [#78176](https://github.com/ClickHouse/ClickHouse/pull/78176) ([Pervakov Grigorii](https://github.com/GrigoryPervakov)). Do not use it: the implementation will change in the next versions.

#### Performance Improvement[​](#performance-improvement-8 "Direct link to Performance Improvement")