2023 Changelog

#### Performance Improvement[​](#performance-improvement-1 "Direct link to Performance Improvement")

- Adaptive timeouts for interacting with S3. The first attempt is made with low send and receive timeouts. [#56314](https://github.com/ClickHouse/ClickHouse/pull/56314) ([Sema Checherinda](https://github.com/CheSema)).
- Increase the default value of `max_concurrent_queries` from 100 to 1000. This makes sense when there is a large number of connecting clients, which are slowly sending or receiving data, so the server is not limited by CPU, or when the number of CPU cores is larger than 100. Also, enable the concurrency control by default, and set the desired number of query processing threads in total as twice the number of CPU cores. It improves performance in scenarios with a very large number of concurrent queries. [#46927](https://github.com/ClickHouse/ClickHouse/pull/46927) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Support parallel evaluation of window functions. Fixes [#34688](https://github.com/ClickHouse/ClickHouse/issues/34688). [#39631](https://github.com/ClickHouse/ClickHouse/pull/39631) ([Dmitry Novik](https://github.com/novikd)).
- `Numbers` table engine (of the `system.numbers` table) now analyzes the condition to generate the needed subset of data, like table's index. [#50909](https://github.com/ClickHouse/ClickHouse/pull/50909) ([JackyWoo](https://github.com/JackyWoo)).
- Improved the performance of filtering by `IN (...)` condition for `Merge` table engine. [#54905](https://github.com/ClickHouse/ClickHouse/pull/54905) ([Nikita Taranov](https://github.com/nickitat)).
- An improvement which takes place when the filesystem cache is full and there are big reads. [#55158](https://github.com/ClickHouse/ClickHouse/pull/55158) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Add ability to disable checksums for S3 to avoid excessive pass over the file (this is controlled by the setting `s3_disable_checksum`). [#55559](https://github.com/ClickHouse/ClickHouse/pull/55559) ([Azat Khuzhin](https://github.com/azat)).
- Now we read synchronously from remote tables when data is in page cache (like we do for local tables). It is faster, it doesn't require synchronisation inside the thread pool, and doesn't hesitate to do `seek`-s on local FS, and reduces CPU wait. [#55841](https://github.com/ClickHouse/ClickHouse/pull/55841) ([Nikita Taranov](https://github.com/nickitat)).
- Optimization for getting value from `map`, `arrayElement`. It will bring about 30% speedup. - reduce the reserved memory - reduce the `resize` call. [#55957](https://github.com/ClickHouse/ClickHouse/pull/55957) ([lgbo](https://github.com/lgbo-ustc)).
- Optimization of multi-stage filtering with AVX-512. The performance experiments of the OnTime dataset on the ICX device (Intel Xeon Platinum 8380 CPU, 80 cores, 160 threads) show that this change could bring the improvements of 7.4%, 5.9%, 4.7%, 3.0%, and 4.6% to the QPS of the query Q2, Q3, Q4, Q5 and Q6 respectively while having no impact on others. [#56079](https://github.com/ClickHouse/ClickHouse/pull/56079) ([Zhiguo Zhou](https://github.com/ZhiguoZh)).
- Limit the number of threads busy inside the query profiler. If there are more - they will skip profiling. [#56105](https://github.com/ClickHouse/ClickHouse/pull/56105) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Decrease the amount of virtual function calls in window functions. [#56120](https://github.com/ClickHouse/ClickHouse/pull/56120) ([Maksim Kita](https://github.com/kitaisreal)).
- Allow recursive Tuple field pruning in ORC data format to speed up scaning. [#56122](https://github.com/ClickHouse/ClickHouse/pull/56122) ([李扬](https://github.com/taiyang-li)).
- Trivial count optimization for `Npy` data format: queries like `select count() from 'data.npy'` will work much more fast because of caching the results. [#56304](https://github.com/ClickHouse/ClickHouse/pull/56304) ([Yarik Briukhovetskyi](https://github.com/yariks5s)).
- Queries with aggregation and a large number of streams will use less amount of memory during the plan's construction. [#57074](https://github.com/ClickHouse/ClickHouse/pull/57074) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Improve performance of executing queries for use cases with many users and highly concurrent queries (>2000 QPS) by optimizing the access to ProcessList. [#57106](https://github.com/ClickHouse/ClickHouse/pull/57106) ([Andrej Hoos](https://github.com/adikus)).
- Trivial improvement on array join, reuse some intermediate results. [#57183](https://github.com/ClickHouse/ClickHouse/pull/57183) ([李扬](https://github.com/taiyang-li)).
- There are cases when stack unwinding was slow. Not anymore. [#57221](https://github.com/ClickHouse/ClickHouse/pull/57221) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
- Now we use default read pool for reading from external storage when `max_streams = 1`. It is beneficial when read prefetches are enabled. [#57334](https://github.com/ClickHouse/ClickHouse/pull/57334) ([Nikita Taranov](https://github.com/nickitat)).
- Keeper improvement: improve memory-usage during startup by delaying log preprocessing. [#55660](https://github.com/ClickHouse/ClickHouse/pull/55660) ([Antonio Andelic](https://github.com/antonio2368)).
- Improved performance of glob matching for `File` and `HDFS` storages. [#56141](https://github.com/ClickHouse/ClickHouse/pull/56141) ([Andrey Zvonov](https://github.com/zvonand)).
- Posting lists in experimental full text indexes are now compressed which reduces their size by 10-30%. [#56226](https://github.com/ClickHouse/ClickHouse/pull/56226) ([Harry Lee](https://github.com/HarryLeeIBM)).
- Parallelise `BackupEntriesCollector` in backups. [#56312](https://github.com/ClickHouse/ClickHouse/pull/56312) ([Kseniia Sumarokova](https://github.com/kssenii)).

#### Improvement[​](#improvement-1 "Direct link to Improvement")