title_wip

#### Performance Improvement[​](#performance-improvement-11 "Direct link to Performance Improvement")

- Coordination for parallel replicas is rewritten for better parallelism and cache locality. It has been tested for linear scalability on hundreds of replicas. It also got support for reading in order. [#57968](https://github.com/ClickHouse/ClickHouse/pull/57968) ([Nikita Taranov](https://github.com/nickitat)).
- Replace HTTP outgoing buffering based with the native ClickHouse buffers. Add bytes counting metrics for interfaces. [#56064](https://github.com/ClickHouse/ClickHouse/pull/56064) ([Yakov Olkhovskiy](https://github.com/yakov-olkhovskiy)).
- Large aggregation states of `uniqExact` will be merged in parallel in distrubuted queries. [#59009](https://github.com/ClickHouse/ClickHouse/pull/59009) ([Nikita Taranov](https://github.com/nickitat)).
- Lower memory usage after reading from `MergeTree` tables. [#59290](https://github.com/ClickHouse/ClickHouse/pull/59290) ([Anton Popov](https://github.com/CurtizJ)).
- Lower memory usage in vertical merges. [#59340](https://github.com/ClickHouse/ClickHouse/pull/59340) ([Anton Popov](https://github.com/CurtizJ)).
- Avoid huge memory consumption during Keeper startup for more cases. [#58455](https://github.com/ClickHouse/ClickHouse/pull/58455) ([Antonio Andelic](https://github.com/antonio2368)).
- Keeper improvement: reduce Keeper's memory usage for stored nodes. [#59002](https://github.com/ClickHouse/ClickHouse/pull/59002) ([Antonio Andelic](https://github.com/antonio2368)).
- More cache-friendly final implementation. Note on the behaviour change: previously queries with `FINAL` modifier that read with a single stream (e.g. `max_threads = 1`) produced sorted output without explicitly provided `ORDER BY` clause. This is no longer guaranteed when `enable_vertical_final = true` (and it is so by default). [#54366](https://github.com/ClickHouse/ClickHouse/pull/54366) ([Duc Canh Le](https://github.com/canhld94)).
- Bypass extra copying in `ReadBufferFromIStream` which is used, e.g., for reading from S3. [#56961](https://github.com/ClickHouse/ClickHouse/pull/56961) ([Nikita Taranov](https://github.com/nickitat)).
- Optimize array element function when input is Array(Map)/Array(Array(Num)/Array(Array(String))/Array(BigInt)/Array(Decimal). The previous implementations did more allocations than needed. The optimization speed up is up to ~6x especially when input type is Array(Map). [#56403](https://github.com/ClickHouse/ClickHouse/pull/56403) ([李扬](https://github.com/taiyang-li)).
- Read column once while reading more than one subcolumn from it in compact parts. [#57631](https://github.com/ClickHouse/ClickHouse/pull/57631) ([Kruglov Pavel](https://github.com/Avogar)).
- Rewrite the AST of `sum(column + constant)` function. This is available as an optimization pass for Analyzer [#57853](https://github.com/ClickHouse/ClickHouse/pull/57853) ([Jiebin Sun](https://github.com/jiebinn)).
- The evaluation of function `match` now utilizes skipping indices `ngrambf_v1` and `tokenbf_v1`. [#57882](https://github.com/ClickHouse/ClickHouse/pull/57882) ([凌涛](https://github.com/lingtaolf)).
- The evaluation of function `match` now utilizes inverted indices. [#58284](https://github.com/ClickHouse/ClickHouse/pull/58284) ([凌涛](https://github.com/lingtaolf)).
- MergeTree `FINAL` does not compare rows from same non-L0 part. [#58142](https://github.com/ClickHouse/ClickHouse/pull/58142) ([Duc Canh Le](https://github.com/canhld94)).
- Speed up iota calls (filling array with consecutive numbers). [#58271](https://github.com/ClickHouse/ClickHouse/pull/58271) ([Raúl Marín](https://github.com/Algunenano)).
- Speedup MIN/MAX for non-numeric types. [#58334](https://github.com/ClickHouse/ClickHouse/pull/58334) ([Raúl Marín](https://github.com/Algunenano)).
- Optimize the combination of filters (like in multi-stage PREWHERE) with BMI2/SSE intrinsics [#58800](https://github.com/ClickHouse/ClickHouse/pull/58800) ([Zhiguo Zhou](https://github.com/ZhiguoZh)).
- Use one thread less in `clickhouse-local`. [#58968](https://github.com/ClickHouse/ClickHouse/pull/58968) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Improve the `multiIf` function performance when the type is Nullable. [#57745](https://github.com/ClickHouse/ClickHouse/pull/57745) ([KevinyhZou](https://github.com/KevinyhZou)).
- Add `SYSTEM JEMALLOC PURGE` for purging unused jemalloc pages, `SYSTEM JEMALLOC [ ENABLE | DISABLE | FLUSH ] PROFILE` for controlling jemalloc profile if the profiler is enabled. Add jemalloc-related 4LW command in Keeper: `jmst` for dumping jemalloc stats, `jmfp`, `jmep`, `jmdp` for controlling jemalloc profile if the profiler is enabled. [#58665](https://github.com/ClickHouse/ClickHouse/pull/58665) ([Antonio Andelic](https://github.com/antonio2368)).
- Lower memory consumption in backups to S3. [#58962](https://github.com/ClickHouse/ClickHouse/pull/58962) ([Vitaly Baranov](https://github.com/vitlibar)).

#### Improvement[​](#improvement-11 "Direct link to Improvement")