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### MergeTree and storage optimizations[​](#mergetree-and-storage-optimizations "Direct link to MergeTree and storage optimizations")

- Add optional `.size` subcolumn serialization for top-level String columns in MergeTree tables to improve compression and enable efficient subcolumn access. Introduce new MergeTree settings for serialization version control and expression optimization for empty strings. [#82850](https://github.com/ClickHouse/ClickHouse/pull/82850) ([Amos Bird](https://github.com/amosbird)).
- Reduce memory allocation and memory copy when select from an aggregating merge tree table with FINAL when the table has columns with type `SimpleAggregateFunction(anyLast)`. [#84428](https://github.com/ClickHouse/ClickHouse/pull/84428) ([Duc Canh Le](https://github.com/canhld94)).
- Improved performance of vertical merges after executing a lightweight delete. [#86169](https://github.com/ClickHouse/ClickHouse/pull/86169) ([Anton Popov](https://github.com/CurtizJ)).
- Improves performance of fast queries with lots of parts in table (by optimizing `MarkRanges` by using `devector` over `deque`). [#86933](https://github.com/ClickHouse/ClickHouse/pull/86933) ([Azat Khuzhin](https://github.com/azat)).
- Improved performance of applying patch parts in join mode. [#87094](https://github.com/ClickHouse/ClickHouse/pull/87094) ([Anton Popov](https://github.com/CurtizJ)).
- Enable saving marks in cache and avoid direct IO for the MergeTreeLazy reader. [#87989](https://github.com/ClickHouse/ClickHouse/pull/87989) ([Nikita Taranov](https://github.com/nickitat)).
- SELECT query with `FINAL` clause on.a `ReplacingMergeTree` table with the `is_deleted` column now executes faster because of improved parallelization from 2 existing optimizations : 1) `do_not_merge_across_partitions_select_final` optimization for partitions of the table that have only a single `part` 2) Split other selected ranges of the table into `intersecting / non-intersecting` and only intersecting ranges have to pass through FINAL merging transform. [#88090](https://github.com/ClickHouse/ClickHouse/pull/88090) ([Shankar Iyer](https://github.com/shankar-iyer)).

### Aggregation and GROUP BY optimizations[​](#aggregation-and-group-by-optimizations "Direct link to Aggregation and GROUP BY optimizations")

- Fix performance degradation caused by a large serialized key while grouping by multiple string/number columns. Close <https://github.com/ClickHouse/ClickHouse/pull/83884#issuecomment-3187972297> cc @mkmkme . It is a follow-up of <https://github.com/ClickHouse/ClickHouse/pull/83884>. [#85924](https://github.com/ClickHouse/ClickHouse/pull/85924) ([李扬](https://github.com/taiyang-li)).
- RadixSort: Help the compiler use SIMD and the CPU do better prefetching. Uses dynamic dispatch to use software prefetching with Intel CPUs only. Continues the work by @taiyang-li in <https://github.com/ClickHouse/ClickHouse/pull/77029>. [#86378](https://github.com/ClickHouse/ClickHouse/pull/86378) ([Raúl Marín](https://github.com/Algunenano)).

### Index and text search optimizations[​](#index-and-text-search-optimizations "Direct link to Index and text search optimizations")

- Improved performance of building text index for documents that contain mostly non-frequent tokens. [#87546](https://github.com/ClickHouse/ClickHouse/pull/87546) ([Anton Popov](https://github.com/CurtizJ)).

### Data lake optimizations[​](#data-lake-optimizations "Direct link to Data lake optimizations")

- Read in order for Iceberg. [#88454](https://github.com/ClickHouse/ClickHouse/pull/88454) ([scanhex12](https://github.com/scanhex12)).

### Internal optimizations[​](#internal-optimizations "Direct link to Internal optimizations")

- Improvements to DB::SharedMutex. [#87491](https://github.com/ClickHouse/ClickHouse/pull/87491) ([Raúl Marín](https://github.com/Algunenano)).
- Speed up the common case of Field destructor. [#87631](https://github.com/ClickHouse/ClickHouse/pull/87631) ([Raúl Marín](https://github.com/Algunenano)).
- Reduce the impact of not using fail points. [#88196](https://github.com/ClickHouse/ClickHouse/pull/88196) ([Raúl Marín](https://github.com/Algunenano)).

## Improvements[​](#improvements "Direct link to Improvements")

### Query optimization and execution[​](#query-optimization-and-execution "Direct link to Query optimization and execution")