### ClickHouse release v20.8.14.4-lts FIXME as compared to v20.8.13.15-lts

#### Improvement
* Backported in [#21235](https://github.com/ClickHouse/ClickHouse/issues/21235): The value of MYSQL_OPT_RECONNECT option can now be controlled by "opt_reconnect" parameter in the config section of mysql replica. [#19998](https://github.com/ClickHouse/ClickHouse/pull/19998) ([Alexander Kazakov](https://github.com/Akazz)).
* Backported in [#21203](https://github.com/ClickHouse/ClickHouse/issues/21203): When loading config for mysql source ClickHouse will now randomize the list of replicas with the same priority to ensure the round-robin logics of picking mysql endpoint. This closes [#20629](https://github.com/ClickHouse/ClickHouse/issues/20629). [#20632](https://github.com/ClickHouse/ClickHouse/pull/20632) ([Alexander Kazakov](https://github.com/Akazz)).
* Backported in [#21336](https://github.com/ClickHouse/ClickHouse/issues/21336): MySQL dictionary source will now retry unexpected connection failures (Lost connection to MySQL server during query) which sometimes happen on SSL/TLS connections. [#21237](https://github.com/ClickHouse/ClickHouse/pull/21237) ([Alexander Kazakov](https://github.com/Akazz)).

#### Bug Fix
* Backported in [#20950](https://github.com/ClickHouse/ClickHouse/issues/20950): 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 [#20948](https://github.com/ClickHouse/ClickHouse/issues/20948): 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 [#20903](https://github.com/ClickHouse/ClickHouse/issues/20903): Fix inserting of `LowCardinality` column to table with `TinyLog` engine. Fixes [#18629](https://github.com/ClickHouse/ClickHouse/issues/18629). [#19010](https://github.com/ClickHouse/ClickHouse/pull/19010) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Backported in [#20899](https://github.com/ClickHouse/ClickHouse/issues/20899): Fix bug when concurrent `ALTER` and `DROP` queries may hang while processing ReplicatedMergeTree table. [#19237](https://github.com/ClickHouse/ClickHouse/pull/19237) ([alesapin](https://github.com/alesapin)).
* Backported in [#20892](https://github.com/ClickHouse/ClickHouse/issues/20892): Fix use-after-free of the CompressedWriteBuffer in Connection after disconnect. [#19599](https://github.com/ClickHouse/ClickHouse/pull/19599) ([Azat Khuzhin](https://github.com/azat)).
* Backported in [#20888](https://github.com/ClickHouse/ClickHouse/issues/20888): Fix rare bug when some replicated operations (like mutation) cannot process some parts after data corruption. Fixes [#19593](https://github.com/ClickHouse/ClickHouse/issues/19593). [#19702](https://github.com/ClickHouse/ClickHouse/pull/19702) ([alesapin](https://github.com/alesapin)).
* Backported in [#21049](https://github.com/ClickHouse/ClickHouse/issues/21049): Fix usage of `-Distinct` combinator with `-State` combinator in aggregate functions. [#20866](https://github.com/ClickHouse/ClickHouse/pull/20866) ([Anton Popov](https://github.com/CurtizJ)).
* Backported in [#21130](https://github.com/ClickHouse/ClickHouse/issues/21130): Fixed behaviour, when `ALTER MODIFY COLUMN` created mutation, that will knowingly fail. [#21007](https://github.com/ClickHouse/ClickHouse/pull/21007) ([Anton Popov](https://github.com/CurtizJ)).
* Backported in [#21159](https://github.com/ClickHouse/ClickHouse/issues/21159): Fix `input_format_null_as_default` take effective when types are nullable. This fixes [#21116](https://github.com/ClickHouse/ClickHouse/issues/21116) . [#21121](https://github.com/ClickHouse/ClickHouse/pull/21121) ([Amos Bird](https://github.com/amosbird)).
* Backported in [#21378](https://github.com/ClickHouse/ClickHouse/issues/21378): Fix error `Bad cast from type ... to DB::ColumnLowCardinality` while inserting into table with `LowCardinality` column from `Values` format. Fixes [#21140](https://github.com/ClickHouse/ClickHouse/issues/21140). [#21357](https://github.com/ClickHouse/ClickHouse/pull/21357) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
