title_wip

- Enables `POPULATE` for `WINDOW VIEW`. [#36945](https://github.com/ClickHouse/ClickHouse/pull/36945) ([vxider](https://github.com/Vxider)).
- `ALTER TABLE ... MODIFY QUERY` support for `WINDOW VIEW`. [#37188](https://github.com/ClickHouse/ClickHouse/pull/37188) ([vxider](https://github.com/Vxider)).
- This PR changes the behavior of the `ENGINE` syntax in `WINDOW VIEW`, to make it like in `MATERIALIZED VIEW`. [#37214](https://github.com/ClickHouse/ClickHouse/pull/37214) ([vxider](https://github.com/Vxider)).

#### Performance Improvement[​](#performance-improvement-6 "Direct link to Performance Improvement")

- Added numerous optimizations for ARM NEON [#38093](https://github.com/ClickHouse/ClickHouse/pull/38093)([Daniel Kutenin](https://github.com/danlark1)), ([Alexandra Pilipyuk](https://github.com/chalice19)) Note: if you run different ClickHouse versions on a cluster with ARM CPU and use distributed queries with GROUP BY multiple keys of fixed-size type that fit in 256 bits but don't fit in 64 bits, the result of the aggregation query will be wrong during upgrade. Workaround: upgrade with downtime instead of a rolling upgrade.
- Improve performance and memory usage for select of subset of columns for formats Native, Protobuf, CapnProto, JSONEachRow, TSKV, all formats with suffixes WithNames/WithNamesAndTypes. Previously while selecting only subset of columns from files in these formats all columns were read and stored in memory. Now only required columns are read. This PR enables setting `input_format_skip_unknown_fields` by default, because otherwise in case of select of subset of columns exception will be thrown. [#37192](https://github.com/ClickHouse/ClickHouse/pull/37192) ([Kruglov Pavel](https://github.com/Avogar)).
- Now more filters can be pushed down for join. [#37472](https://github.com/ClickHouse/ClickHouse/pull/37472) ([Amos Bird](https://github.com/amosbird)).
- Load marks for only necessary columns when reading wide parts. [#36879](https://github.com/ClickHouse/ClickHouse/pull/36879) ([Anton Kozlov](https://github.com/tonickkozlov)).
- Improved performance of aggregation in case, when sparse columns (can be enabled by experimental setting `ratio_of_defaults_for_sparse_serialization` in `MergeTree` tables) are used as arguments in aggregate functions. [#37617](https://github.com/ClickHouse/ClickHouse/pull/37617) ([Anton Popov](https://github.com/CurtizJ)).
- Optimize function `COALESCE` with two arguments. [#37666](https://github.com/ClickHouse/ClickHouse/pull/37666) ([Anton Popov](https://github.com/CurtizJ)).
- Replace `multiIf` to `if` in case when `multiIf` has only one condition, because function `if` is more performant. [#37695](https://github.com/ClickHouse/ClickHouse/pull/37695) ([Anton Popov](https://github.com/CurtizJ)).
- Improve performance of `dictGetDescendants`, `dictGetChildren` functions, create temporary parent to children hierarchical index per query, not per function call during query. Allow to specify `BIDIRECTIONAL` for `HIERARHICAL` attributes, dictionary will maintain parent to children index in memory, that way functions `dictGetDescendants`, `dictGetChildren` will not create temporary index per query. Closes [#32481](https://github.com/ClickHouse/ClickHouse/issues/32481). [#37148](https://github.com/ClickHouse/ClickHouse/pull/37148) ([Maksim Kita](https://github.com/kitaisreal)).
- Aggregates state destruction now may be posted on a thread pool. For queries with LIMIT and big state it provides significant speedup, e.g. `select uniq(number) from numbers_mt(1e7) group by number limit 100` became around 2.5x faster. [#37855](https://github.com/ClickHouse/ClickHouse/pull/37855) ([Nikita Taranov](https://github.com/nickitat)).
- Improve sort performance by single column. [#37195](https://github.com/ClickHouse/ClickHouse/pull/37195) ([Maksim Kita](https://github.com/kitaisreal)).
- Improve performance of single column sorting using sorting queue specializations. [#37990](https://github.com/ClickHouse/ClickHouse/pull/37990) ([Maksim Kita](https://github.com/kitaisreal)).
- Improved performance on array norm and distance functions 2x-4x times. [#37394](https://github.com/ClickHouse/ClickHouse/pull/37394) ([Alexander Gololobov](https://github.com/davenger)).
- Improve performance of number comparison functions using dynamic dispatch. [#37399](https://github.com/ClickHouse/ClickHouse/pull/37399) ([Maksim Kita](https://github.com/kitaisreal)).
- Improve performance of ORDER BY with LIMIT. [#37481](https://github.com/ClickHouse/ClickHouse/pull/37481) ([Maksim Kita](https://github.com/kitaisreal)).
- Improve performance of `hasAll` function using dynamic dispatch infrastructure. [#37484](https://github.com/ClickHouse/ClickHouse/pull/37484) ([Maksim Kita](https://github.com/kitaisreal)).
- Improve performance of `greatCircleAngle`, `greatCircleDistance`, `geoDistance` functions. [#37524](https://github.com/ClickHouse/ClickHouse/pull/37524) ([Maksim Kita](https://github.com/kitaisreal)).
- Improve performance of insert into MergeTree if there are multiple columns in ORDER BY. [#35762](https://github.com/ClickHouse/ClickHouse/pull/35762) ([Maksim Kita](https://github.com/kitaisreal)).
- Fix excessive CPU usage in background when there are a lot of tables. [#38028](https://github.com/ClickHouse/ClickHouse/pull/38028) ([Maksim Kita](https://github.com/kitaisreal)).
- Improve performance of `not` function using dynamic dispatch. [#38058](https://github.com/ClickHouse/ClickHouse/pull/38058) ([Maksim Kita](https://github.com/kitaisreal)).
- Optimized the internal caching of re2 patterns which occur e.g. in LIKE and MATCH functions. [#37544](https://github.com/ClickHouse/ClickHouse/pull/37544) ([Robert Schulze](https://github.com/rschu1ze)).
- Improve filter bitmask generator function all in one with AVX-512 instructions. [#37588](https://github.com/ClickHouse/ClickHouse/pull/37588) ([yaqi-zhao](https://github.com/yaqi-zhao)).
- Apply read method `threadpool` for Hive integration engine. This will significantly speed up reading. [#36328](https://github.com/ClickHouse/ClickHouse/pull/36328) ([李扬](https://github.com/taiyang-li)).
- When all the columns to read are partition keys, construct columns by the file's row number without real reading the Hive file. [#37103](https://github.com/ClickHouse/ClickHouse/pull/37103) ([lgbo](https://github.com/lgbo-ustc)).
- Support multi disks for caching hive files. [#37279](https://github.com/ClickHouse/ClickHouse/pull/37279) ([lgbo](https://github.com/lgbo-ustc)).
- Limiting the maximum cache usage per query can effectively prevent cache pool contamination. [Related Issues](https://github.com/ClickHouse/ClickHouse/issues/28961). [#37859](https://github.com/ClickHouse/ClickHouse/pull/37859) ([Han Shukai](https://github.com/KinderRiven)).
- Currently clickhouse directly downloads all remote files to the local cache (even if they are only read once), which will frequently cause IO of the local hard disk. In some scenarios, these IOs may not be necessary and may easily cause negative optimization. As shown in the figure below, when we run SSB Q1-Q4, the performance of the cache has caused negative optimization. [#37516](https://github.com/ClickHouse/ClickHouse/pull/37516) ([Han Shukai](https://github.com/KinderRiven)).
- Allow to prune the list of files via virtual columns such as `_file` and `_path` when reading from S3. This is for [#37174](https://github.com/ClickHouse/ClickHouse/issues/37174) , [#23494](https://github.com/ClickHouse/ClickHouse/issues/23494). [#37356](https://github.com/ClickHouse/ClickHouse/pull/37356) ([Amos Bird](https://github.com/amosbird)).
- In function: CompressedWriteBuffer::nextImpl(), there is an unnecessary write-copy step that would happen frequently during inserting data. Below shows the differentiation with this patch: - Before: 1. Compress "working\_buffer" into "compressed\_buffer" 2. write-copy into "out" - After: Directly Compress "working\_buffer" into "out". [#37242](https://github.com/ClickHouse/ClickHouse/pull/37242) ([jasperzhu](https://github.com/jinjunzh)).

#### Improvement[​](#improvement-6 "Direct link to Improvement")