ClickHouse/docs/changelogs/v20.10.6.27-stable.md

### ClickHouse release v20.10.6.27-stable FIXME as compared to v20.10.5.10-stable

#### Performance Improvement
* Backported in [#17591](https://github.com/ClickHouse/ClickHouse/issues/17591): Fix performance of reading from `Merge` tables over huge number of `MergeTree` tables. Fixes [#7748](https://github.com/ClickHouse/ClickHouse/issues/7748). [#16988](https://github.com/ClickHouse/ClickHouse/pull/16988) ([Anton Popov](https://github.com/CurtizJ)).

#### Bug Fix
* Backported in [#17157](https://github.com/ClickHouse/ClickHouse/issues/17157): Fixed uncontrolled growth of TDigest. [#16680](https://github.com/ClickHouse/ClickHouse/pull/16680) ([hrissan](https://github.com/hrissan)).
* Backported in [#17314](https://github.com/ClickHouse/ClickHouse/issues/17314): Return number of affected rows for INSERT queries via MySQL protocol. Previously ClickHouse used to always return 0, it's fixed. Fixes [#16605](https://github.com/ClickHouse/ClickHouse/issues/16605). [#16715](https://github.com/ClickHouse/ClickHouse/pull/16715) ([Winter Zhang](https://github.com/zhang2014)).
* Backported in [#17341](https://github.com/ClickHouse/ClickHouse/issues/17341): TODO. [#16866](https://github.com/ClickHouse/ClickHouse/pull/16866) ([Alexander Tokmakov](https://github.com/tavplubix)).
* Backported in [#17587](https://github.com/ClickHouse/ClickHouse/issues/17587): Fix optimization of group by with enabled setting `optimize_aggregators_of_group_by_keys` and joins. Fixes [#12604](https://github.com/ClickHouse/ClickHouse/issues/12604). [#16951](https://github.com/ClickHouse/ClickHouse/pull/16951) ([Anton Popov](https://github.com/CurtizJ)).
* Backported in [#17594](https://github.com/ClickHouse/ClickHouse/issues/17594): Fix order by optimization with monotonous functions. Fixes [#16107](https://github.com/ClickHouse/ClickHouse/issues/16107). [#16956](https://github.com/ClickHouse/ClickHouse/pull/16956) ([Anton Popov](https://github.com/CurtizJ)).
* Backported in [#17197](https://github.com/ClickHouse/ClickHouse/issues/17197): Avoid unnecessary network errors for remote queries which may be cancelled while execution, like queries with `LIMIT`. [#17006](https://github.com/ClickHouse/ClickHouse/pull/17006) ([Azat Khuzhin](https://github.com/azat)).
* Backported in [#17431](https://github.com/ClickHouse/ClickHouse/issues/17431): Bug fix for funciton fuzzBits, related issue: [#16980](https://github.com/ClickHouse/ClickHouse/issues/16980). [#17051](https://github.com/ClickHouse/ClickHouse/pull/17051) ([hexiaoting](https://github.com/hexiaoting)).
* Backported in [#17130](https://github.com/ClickHouse/ClickHouse/issues/17130): Fixed crash on `CREATE TABLE ... AS some_table` query when `some_table` was created `AS table_function()` Fixes [#16944](https://github.com/ClickHouse/ClickHouse/issues/16944). [#17072](https://github.com/ClickHouse/ClickHouse/pull/17072) ([Alexander Tokmakov](https://github.com/tavplubix)).
* Backported in [#17193](https://github.com/ClickHouse/ClickHouse/issues/17193): Fix ColumnConst comparison which leads to crash. This fixed [#17088](https://github.com/ClickHouse/ClickHouse/issues/17088) . [#17135](https://github.com/ClickHouse/ClickHouse/pull/17135) ([Amos Bird](https://github.com/amosbird)).
* Backported in [#17395](https://github.com/ClickHouse/ClickHouse/issues/17395): Fix [#15235](https://github.com/ClickHouse/ClickHouse/issues/15235). When clickhouse-copier handle non-partitioned table, throws segfault error. [#17248](https://github.com/ClickHouse/ClickHouse/pull/17248) ([Qi Chen](https://github.com/kaka11chen)).
* Backported in [#17407](https://github.com/ClickHouse/ClickHouse/issues/17407): Fix set index invalidation when there are const columns in the subquery. This fixes [#17246](https://github.com/ClickHouse/ClickHouse/issues/17246) . [#17249](https://github.com/ClickHouse/ClickHouse/pull/17249) ([Amos Bird](https://github.com/amosbird)).
* Backported in [#17487](https://github.com/ClickHouse/ClickHouse/issues/17487): Fix crash while reading from `JOIN` table with `LowCardinality` types. Fixes [#17228](https://github.com/ClickHouse/ClickHouse/issues/17228). [#17397](https://github.com/ClickHouse/ClickHouse/pull/17397) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Backported in [#17491](https://github.com/ClickHouse/ClickHouse/issues/17491): Fix duplicates after `DISTINCT` which were possible because of incorrect optimization. Fixes [#17294](https://github.com/ClickHouse/ClickHouse/issues/17294). [#17296](https://github.com/ClickHouse/ClickHouse/pull/17296) ([li chengxiang](https://github.com/chengxianglibra)). [#17439](https://github.com/ClickHouse/ClickHouse/pull/17439) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Backported in [#17524](https://github.com/ClickHouse/ClickHouse/issues/17524): Fix `ORDER BY` with enabled setting `optimize_redundant_functions_in_order_by`. [#17471](https://github.com/ClickHouse/ClickHouse/pull/17471) ([Anton Popov](https://github.com/CurtizJ)).
* Backported in [#17532](https://github.com/ClickHouse/ClickHouse/issues/17532): Fix bug when mark cache size was underestimated by clickhouse. It may happen when there are a lot of tiny files with marks. [#17496](https://github.com/ClickHouse/ClickHouse/pull/17496) ([alesapin](https://github.com/alesapin)).
* Backported in [#17626](https://github.com/ClickHouse/ClickHouse/issues/17626): Fix alter query hang when the corresponding mutation was killed on the different replica. Fixes [#16953](https://github.com/ClickHouse/ClickHouse/issues/16953). [#17499](https://github.com/ClickHouse/ClickHouse/pull/17499) ([alesapin](https://github.com/alesapin)).
* Backported in [#17609](https://github.com/ClickHouse/ClickHouse/issues/17609): When clickhouse-client is used in interactive mode with multiline queries, single line comment was erronously extended till the end of query. This fixes [#13654](https://github.com/ClickHouse/ClickHouse/issues/13654). [#17565](https://github.com/ClickHouse/ClickHouse/pull/17565) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
* Backported in [#17698](https://github.com/ClickHouse/ClickHouse/issues/17698): In might be determined incorrectly if cluster is circular- (cross-) replicated or not when executing `ON CLUSTER` query due to race condition when `pool_size` > 1. It's fixed. [#17640](https://github.com/ClickHouse/ClickHouse/pull/17640) ([Alexander Tokmakov](https://github.com/tavplubix)).
* Backported in [#17730](https://github.com/ClickHouse/ClickHouse/issues/17730): Fixed `Function not implemented` error when executing `RENAME` query in `Atomic` database with ClickHouse running on Windows Subsystem for Linux. Fixes [#17661](https://github.com/ClickHouse/ClickHouse/issues/17661). [#17664](https://github.com/ClickHouse/ClickHouse/pull/17664) ([Alexander Tokmakov](https://github.com/tavplubix)).
* Backported in [#17783](https://github.com/ClickHouse/ClickHouse/issues/17783): Fixed problem when ClickHouse fails to resume connection to MySQL servers. [#17681](https://github.com/ClickHouse/ClickHouse/pull/17681) ([Alexander Kazakov](https://github.com/Akazz)).
* Backported in [#17816](https://github.com/ClickHouse/ClickHouse/issues/17816): Do not restore parts from WAL if `in_memory_parts_enable_wal` is disabled. [#17802](https://github.com/ClickHouse/ClickHouse/pull/17802) ([detailyang](https://github.com/detailyang)).

#### Build/Testing/Packaging Improvement
* Backported in [#17289](https://github.com/ClickHouse/ClickHouse/issues/17289): Update embedded timezone data to version 2020d (also update cctz to the latest master). [#17204](https://github.com/ClickHouse/ClickHouse/pull/17204) ([filimonov](https://github.com/filimonov)).