### ClickHouse release v20.12.6.29-stable FIXME as compared to v20.12.5.18-stable

#### Bug Fix
* Backported in [#19984](https://github.com/ClickHouse/ClickHouse/issues/19984): Background thread which executes `ON CLUSTER` queries might hang waiting for dropped replicated table to do something. It's fixed. [#19684](https://github.com/ClickHouse/ClickHouse/pull/19684) ([yiguolei](https://github.com/yiguolei)).
* Backported in [#20240](https://github.com/ClickHouse/ClickHouse/issues/20240): Fix a bug that moving pieces to destination table may failed in case of launching multiple clickhouse-copiers. [#19743](https://github.com/ClickHouse/ClickHouse/pull/19743) ([madianjun](https://github.com/mdianjun)).
* Backported in [#20080](https://github.com/ClickHouse/ClickHouse/issues/20080): Fix starting the server with tables having default expressions containing dictGet(). Allow getting return type of dictGet() without loading dictionary. [#19805](https://github.com/ClickHouse/ClickHouse/pull/19805) ([Vitaly Baranov](https://github.com/vitlibar)).
* Backported in [#20298](https://github.com/ClickHouse/ClickHouse/issues/20298): * Bugfix in StorageJoin. [#20079](https://github.com/ClickHouse/ClickHouse/pull/20079) ([Vladimir C](https://github.com/vdimir)).
* Backported in [#20391](https://github.com/ClickHouse/ClickHouse/issues/20391): The `MongoDB` table engine now establishes connection only when it's going to read data. `ATTACH TABLE` won't try to connect anymore. [#20110](https://github.com/ClickHouse/ClickHouse/pull/20110) ([Vitaly Baranov](https://github.com/vitlibar)).
* Backported in [#20328](https://github.com/ClickHouse/ClickHouse/issues/20328): Fix rare server crash on config reload during the shutdown. Fixes [#19689](https://github.com/ClickHouse/ClickHouse/issues/19689). [#20224](https://github.com/ClickHouse/ClickHouse/pull/20224) ([alesapin](https://github.com/alesapin)).
* Backported in [#20332](https://github.com/ClickHouse/ClickHouse/issues/20332): Restrict to `DROP` or `RENAME` version column of `*CollapsingMergeTree` and `ReplacingMergeTree` table engines. [#20300](https://github.com/ClickHouse/ClickHouse/pull/20300) ([alesapin](https://github.com/alesapin)).
* Backported in [#20364](https://github.com/ClickHouse/ClickHouse/issues/20364): Fix too often retries of failed background tasks for `ReplicatedMergeTree` table engines family. This could lead to too verbose logging and increased CPU load. Fixes [#20203](https://github.com/ClickHouse/ClickHouse/issues/20203). [#20335](https://github.com/ClickHouse/ClickHouse/pull/20335) ([alesapin](https://github.com/alesapin)).
* Backported in [#20377](https://github.com/ClickHouse/ClickHouse/issues/20377): Fix null dereference with `join_use_nulls=1`. [#20344](https://github.com/ClickHouse/ClickHouse/pull/20344) ([Azat Khuzhin](https://github.com/azat)).
* Backported in [#20360](https://github.com/ClickHouse/ClickHouse/issues/20360): Avoid invalid dereference in RANGE_HASHED() dictionary. [#20345](https://github.com/ClickHouse/ClickHouse/pull/20345) ([Azat Khuzhin](https://github.com/azat)).

#### NO CL ENTRY

* NO CL ENTRY:  'Revert "Backport [#20224](https://github.com/ClickHouse/ClickHouse/issues/20224) to 20.12: Fix access control manager destruction order"'. [#20396](https://github.com/ClickHouse/ClickHouse/pull/20396) ([alesapin](https://github.com/alesapin)).
