### ClickHouse release v20.8.15.11-lts FIXME as compared to v20.8.14.4-lts

#### Bug Fix
* Backported in [#21627](https://github.com/ClickHouse/ClickHouse/issues/21627): Fix max_distributed_connections (affects `prefer_localhost_replica=1` and `max_threads!=max_distributed_connections`). [#17848](https://github.com/ClickHouse/ClickHouse/pull/17848) ([Azat Khuzhin](https://github.com/azat)).
* Backported in [#21626](https://github.com/ClickHouse/ClickHouse/issues/21626): Join tries to materialize const columns, but our code waits for them in other places. [#18982](https://github.com/ClickHouse/ClickHouse/pull/18982) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Backported in [#21409](https://github.com/ClickHouse/ClickHouse/issues/21409): Now mutations allowed only for table engines that support them (MergeTree family, Memory, MaterializedView). Other engines will report a more clear error. Fixes [#21168](https://github.com/ClickHouse/ClickHouse/issues/21168). [#21183](https://github.com/ClickHouse/ClickHouse/pull/21183) ([alesapin](https://github.com/alesapin)).
* Backported in [#22190](https://github.com/ClickHouse/ClickHouse/issues/22190): Fixed race on SSL object inside SecureSocket in Poco. [#21456](https://github.com/ClickHouse/ClickHouse/pull/21456) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Backported in [#21547](https://github.com/ClickHouse/ClickHouse/issues/21547): Fix a deadlock in `ALTER DELETE` mutations for non replicated MergeTree table engines when the predicate contains the table itself. Fixes [#20558](https://github.com/ClickHouse/ClickHouse/issues/20558). [#21477](https://github.com/ClickHouse/ClickHouse/pull/21477) ([alesapin](https://github.com/alesapin)).
* Backported in [#22284](https://github.com/ClickHouse/ClickHouse/issues/22284): Fix bug for ReplicatedMerge table engines when `ALTER MODIFY COLUMN` query doesn't change the type of decimal column if its size (32 bit or 64 bit) doesn't change. [#21728](https://github.com/ClickHouse/ClickHouse/pull/21728) ([alesapin](https://github.com/alesapin)).
* Backported in [#22282](https://github.com/ClickHouse/ClickHouse/issues/22282): Docker entrypoint: avoid chown of `.` in case when `LOG_PATH` is empty. Closes [#22100](https://github.com/ClickHouse/ClickHouse/issues/22100). [#22102](https://github.com/ClickHouse/ClickHouse/pull/22102) ([filimonov](https://github.com/filimonov)).
* Backported in [#22279](https://github.com/ClickHouse/ClickHouse/issues/22279): Fix waiting for `OPTIMIZE` and `ALTER` queries for `ReplicatedMergeTree` table engines. Now the query will not hang when the table was detached or restarted. [#22118](https://github.com/ClickHouse/ClickHouse/pull/22118) ([alesapin](https://github.com/alesapin)).
* Backported in [#22370](https://github.com/ClickHouse/ClickHouse/issues/22370): Now clickhouse will not throw `LOGICAL_ERROR` exception when we try to mutate the already covered part. Fixes [#22013](https://github.com/ClickHouse/ClickHouse/issues/22013). [#22291](https://github.com/ClickHouse/ClickHouse/pull/22291) ([alesapin](https://github.com/alesapin)).

#### NO CL ENTRY

* NO CL ENTRY:  'Revert "Backport [#17848](https://github.com/ClickHouse/ClickHouse/issues/17848) to 20.8: Fix max_distributed_connections"'. [#21940](https://github.com/ClickHouse/ClickHouse/pull/21940) ([Maksim Kita](https://github.com/kitaisreal)).
