2025 Changelog

- Optimize `largestTriangleThreeBuckets` by removing temporary data. [#84479](https://github.com/ClickHouse/ClickHouse/pull/84479) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Optimize string deserialization by simplifying the code. Closes [#38564](https://github.com/ClickHouse/ClickHouse/issues/38564). [#84561](https://github.com/ClickHouse/ClickHouse/pull/84561) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Fixed the calculation of the minimal task size for parallel replicas. [#84752](https://github.com/ClickHouse/ClickHouse/pull/84752) ([Nikita Taranov](https://github.com/nickitat)).
- Improved performance of applying patch parts in `Join` mode. [#85040](https://github.com/ClickHouse/ClickHouse/pull/85040) ([Anton Popov](https://github.com/CurtizJ)).
- Remove zero byte. Closes [#85062](https://github.com/ClickHouse/ClickHouse/issues/85062). A few minor bugs were fixed. Functions `structureToProtobufSchema`, `structureToCapnProtoSchema` didn't correctly put a zero-terminating byte and were using a newline instead of it. That was leading to a missing newline in the output, and could lead to buffer overflows while using other functions that depend on the zero byte (such as `logTrace`, `demangle`, `extractURLParameter`, `toStringCutToZero`, and `encrypt`/`decrypt`). The `regexp_tree` dictionary layout didn't support processing strings with zero bytes. The `formatRowNoNewline` function, called with `Values` format or with any other format without a newline at the end of rows, erroneously cuts the last character of the output. Function `stem` contained an exception-safety error that could lead to a memory leak in a very rare scenario. The `initcap` function worked in the wrong way for `FixedString` arguments: it didn't recognize the start of the word at the start of the string if the previous string in a block ended with a word character. Fixed a security vulnerability of the Apache `ORC` format, which could lead to the exposure of uninitialized memory. Changed behavior of the function `replaceRegexpAll` and the corresponding alias, `REGEXP_REPLACE`: now it can do an empty match at the end of the string even if the previous match processed the whole string, such as in the case of `^a*|a*$` or `^|.*` - this corresponds to the semantic of JavaScript, Perl, Python, PHP, Ruby, but differs to the semantic of PostgreSQL. Implementation of many functions has been simplified and optimized. Documentation for several functions was wrong and has now been fixed. Keep in mind that the output of `byteSize` for String columns and complex types, which consisted of String columns, has changed (from 9 bytes per empty string to 8 bytes per empty string), and this is normal. [#85063](https://github.com/ClickHouse/ClickHouse/pull/85063) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Optimize the materialization of constants in cases when we do this materialization only to return a single row. [#85071](https://github.com/ClickHouse/ClickHouse/pull/85071) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Improve parallel files processing with delta-kernel-rs backend. [#85642](https://github.com/ClickHouse/ClickHouse/pull/85642) ([Azat Khuzhin](https://github.com/azat)).
- A new setting, enable\_add\_distinct\_to\_in\_subqueries, has been introduced. When enabled, ClickHouse will automatically add DISTINCT to subqueries in IN clauses for distributed queries. This can significantly reduce the size of temporary tables transferred between shards and improve network efficiency. Note: This is a trade-off—while network transfer is reduced, additional merging (deduplication) work is required on each node. Enable this setting when network transfer is a bottleneck and the merging cost is acceptable. [#81908](https://github.com/ClickHouse/ClickHouse/pull/81908) ([fhw12345](https://github.com/fhw12345)).
- Reduce query memory tracking overhead for executable user-defined functions. [#83929](https://github.com/ClickHouse/ClickHouse/pull/83929) ([Eduard Karacharov](https://github.com/korowa)).
- Implement internal `delta-kernel-rs` filtering (statistics and partition pruning) in storage `DeltaLake`. [#84006](https://github.com/ClickHouse/ClickHouse/pull/84006) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Disable skipping indexes that depend on columns updated on the fly or by patch parts more granularly. Now, skipping indexes are not used only in parts affected by on-the-fly mutations or patch parts; previously, those indexes were disabled for all parts. [#84241](https://github.com/ClickHouse/ClickHouse/pull/84241) ([Anton Popov](https://github.com/CurtizJ)).
- Allocate the minimum amount of memory needed for encrypted\_buffer for encrypted named collections. [#84432](https://github.com/ClickHouse/ClickHouse/pull/84432) ([Pablo Marcos](https://github.com/pamarcos)).
- Improved support for bloom filter indexes (regular, ngram, and token) to be utilized when the first argument is a constant array (the set) and the second is the indexed column (the subset), enabling more efficient query execution. [#84700](https://github.com/ClickHouse/ClickHouse/pull/84700) ([Doron David](https://github.com/dorki)).
- Reduce contention on storage lock in Keeper. [#84732](https://github.com/ClickHouse/ClickHouse/pull/84732) ([Antonio Andelic](https://github.com/antonio2368)).
- Add missing support of `read_in_order_use_virtual_row` for `WHERE`. It allows to skip reading more parts for queries with filters that were not fully pushed to `PREWHERE`. [#84835](https://github.com/ClickHouse/ClickHouse/pull/84835) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
- Allows asynchronously iterating objects from Iceberg table without storing objects for each data file explicitly. [#85369](https://github.com/ClickHouse/ClickHouse/pull/85369) ([Daniil Ivanik](https://github.com/divanik)).
- Execute non-correlated `EXISTS` as a scalar subquery. This allows using a scalar subquery cache and constant-folding the result, which is helpful for indexes. For compatibility, the new setting `execute_exists_as_scalar_subquery=1` is added. [#85481](https://github.com/ClickHouse/ClickHouse/pull/85481) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).