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Merge pull request #49235 from ClickHouse/alexey-milovidov-patch-7

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Update CHANGELOG.md
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Alexey Milovidov 2023-04-27 00:53:32 +03:00 committed by GitHub
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@ -37,8 +37,7 @@
* Optimize function `mapUpdate`. [#48118](https://github.com/ClickHouse/ClickHouse/pull/48118) ([Anton Popov](https://github.com/CurtizJ)).
* Now an internal query to local replica is sent explicitly and data from it received through loopback interface. Setting `prefer_localhost_replica` is not respected for parallel replicas. This is needed for better scheduling and makes the code cleaner: the initiator is only responsible for coordinating of the reading process and merging results, continuously answering for requests while all the secondary queries read the data. Note: Using loopback interface is not so performant, otherwise some replicas could starve for tasks which could lead to even slower query execution and not utilizing all possible resources. The initialization of the coordinator is now even more lazy. All incoming requests contain the information about the reading algorithm we initialize the coordinator with it when first request comes. If any replica decides to read with a different algorithm–an exception will be thrown and a query will be aborted. [#48246](https://github.com/ClickHouse/ClickHouse/pull/48246) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Do not build set for the right side of `IN` clause with subquery when it is used only for analysis of skip indexes, and they are disabled by setting (`use_skip_indexes=0`). Previously it might affect the performance of queries. [#48299](https://github.com/ClickHouse/ClickHouse/pull/48299) ([Anton Popov](https://github.com/CurtizJ)).
* Query processing is parallelized right after reading `FROM file(...)`. Related to [#38755](https://github.com/ClickHouse/ClickHouse/issues/38755). [#48525](https://github.com/ClickHouse/ClickHouse/pull/48525) ([Igor Nikonov](https://github.com/devcrafter)).
* Query processing is parallelized right after reading from a data source. Affected data sources are mostly simple or external storages like table functions `url`, `file`. [#48727](https://github.com/ClickHouse/ClickHouse/pull/48727) ([Igor Nikonov](https://github.com/devcrafter)).
* Query processing is parallelized right after reading `FROM file(...)`. Related to [#38755](https://github.com/ClickHouse/ClickHouse/issues/38755). [#48525](https://github.com/ClickHouse/ClickHouse/pull/48525) ([Igor Nikonov](https://github.com/devcrafter)). Query processing is parallelized right after reading from any data source. Affected data sources are mostly simple or external storages like table functions `url`, `file`. [#48727](https://github.com/ClickHouse/ClickHouse/pull/48727) ([Igor Nikonov](https://github.com/devcrafter)). This is controlled by the setting `parallelize_output_from_storages` which is not enabled by default.
* Lowered contention of ThreadPool mutex (may increase performance for a huge amount of small jobs). [#48750](https://github.com/ClickHouse/ClickHouse/pull/48750) ([Sergei Trifonov](https://github.com/serxa)).
* Reduce memory usage for multiple `ALTER DELETE` mutations. [#48522](https://github.com/ClickHouse/ClickHouse/pull/48522) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Remove the excessive connection attempts if the `skip_unavailable_shards` setting is enabled. [#48771](https://github.com/ClickHouse/ClickHouse/pull/48771) ([Azat Khuzhin](https://github.com/azat)).