### ClickHouse release v20.8.4.11-lts FIXME as compared to v20.8.3.18-stable

#### Improvement
* Backported in [#15569](https://github.com/ClickHouse/ClickHouse/issues/15569): Now it's possible to change the type of version column for `VersionedCollapsingMergeTree` with `ALTER` query. [#15442](https://github.com/ClickHouse/ClickHouse/pull/15442) ([alesapin](https://github.com/alesapin)).

#### Bug Fix
* Backported in [#15017](https://github.com/ClickHouse/ClickHouse/issues/15017): Fixed the incorrect sorting order of `Nullable` column. This fixes [#14344](https://github.com/ClickHouse/ClickHouse/issues/14344). [#14495](https://github.com/ClickHouse/ClickHouse/pull/14495) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Backported in [#14823](https://github.com/ClickHouse/ClickHouse/issues/14823): Fix wrong monotonicity detection for shrunk `Int -> Int` cast of signed types. It might lead to incorrect query result. This bug is unveiled in [#14513](https://github.com/ClickHouse/ClickHouse/issues/14513). [#14783](https://github.com/ClickHouse/ClickHouse/pull/14783) ([Amos Bird](https://github.com/amosbird)).
* Backported in [#15148](https://github.com/ClickHouse/ClickHouse/issues/15148): Fix a problem where the server may get stuck on startup while talking to ZooKeeper, if the configuration files have to be fetched from ZK (using the `from_zk` include option). This fixes [#14814](https://github.com/ClickHouse/ClickHouse/issues/14814). [#14843](https://github.com/ClickHouse/ClickHouse/pull/14843) ([Alexander Kuzmenkov](https://github.com/akuzm)).
* Backported in [#15251](https://github.com/ClickHouse/ClickHouse/issues/15251): Fixed segfault in CacheDictionary [#14837](https://github.com/ClickHouse/ClickHouse/issues/14837). [#14879](https://github.com/ClickHouse/ClickHouse/pull/14879) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Backported in [#14955](https://github.com/ClickHouse/ClickHouse/issues/14955): Fixed `.metadata.tmp File exists` error when using `MaterializeMySQL` database engine. [#14898](https://github.com/ClickHouse/ClickHouse/pull/14898) ([Winter Zhang](https://github.com/zhang2014)).
* Backported in [#14987](https://github.com/ClickHouse/ClickHouse/issues/14987): Publish CPU frequencies per logical core in `system.asynchronous_metrics`. This fixes [#14923](https://github.com/ClickHouse/ClickHouse/issues/14923). [#14924](https://github.com/ClickHouse/ClickHouse/pull/14924) ([Alexander Kuzmenkov](https://github.com/akuzm)).
* Backported in [#14969](https://github.com/ClickHouse/ClickHouse/issues/14969): Fix to make predicate push down work when subquery contains finalizeAggregation function. Fixes [#14847](https://github.com/ClickHouse/ClickHouse/issues/14847). [#14937](https://github.com/ClickHouse/ClickHouse/pull/14937) ([filimonov](https://github.com/filimonov)).
* Backported in [#15053](https://github.com/ClickHouse/ClickHouse/issues/15053): Now settings `number_of_free_entries_in_pool_to_execute_mutation` and `number_of_free_entries_in_pool_to_lower_max_size_of_merge` can be equal to `background_pool_size`. [#14975](https://github.com/ClickHouse/ClickHouse/pull/14975) ([alesapin](https://github.com/alesapin)).
* Backported in [#15077](https://github.com/ClickHouse/ClickHouse/issues/15077): Fix crash in RIGHT or FULL JOIN with join_algorith='auto' when memory limit exceeded and we should change HashJoin with MergeJoin. [#15002](https://github.com/ClickHouse/ClickHouse/pull/15002) ([Artem Zuikov](https://github.com/4ertus2)).
* Backported in [#15102](https://github.com/ClickHouse/ClickHouse/issues/15102): Fixed `Cannot rename ... errno: 22, strerror: Invalid argument` error on DDL query execution in Atomic database when running clickhouse-server in docker on Mac OS. [#15024](https://github.com/ClickHouse/ClickHouse/pull/15024) ([Alexander Tokmakov](https://github.com/tavplubix)).
* Backported in [#15056](https://github.com/ClickHouse/ClickHouse/issues/15056): If function `bar` was called with specifically crafted arguments, buffer overflow was possible. This closes [#13926](https://github.com/ClickHouse/ClickHouse/issues/13926). [#15028](https://github.com/ClickHouse/ClickHouse/pull/15028) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
* Backported in [#15049](https://github.com/ClickHouse/ClickHouse/issues/15049): We already use padded comparison between String and FixedString (https://github.com/ClickHouse/ClickHouse/blob/master/src/Functions/FunctionsComparison.h#L333). This PR applies the same logic to field comparison which corrects the usage of FixedString as primary keys. This fixes [#14908](https://github.com/ClickHouse/ClickHouse/issues/14908). [#15033](https://github.com/ClickHouse/ClickHouse/pull/15033) ([Amos Bird](https://github.com/amosbird)).
* Backported in [#15142](https://github.com/ClickHouse/ClickHouse/issues/15142): Fixes `Data compressed with different methods` in `join_algorithm='auto'`. Keep LowCardinality as type for left table join key in `join_algorithm='partial_merge'`. [#15088](https://github.com/ClickHouse/ClickHouse/pull/15088) ([Artem Zuikov](https://github.com/4ertus2)).
* Backported in [#15208](https://github.com/ClickHouse/ClickHouse/issues/15208): Adjust decimals field size in mysql column definition packet. [#15152](https://github.com/ClickHouse/ClickHouse/pull/15152) ([maqroll](https://github.com/maqroll)).
* Backported in [#15222](https://github.com/ClickHouse/ClickHouse/issues/15222): Fix bug in table engine `Buffer` which doesn't allow to insert data of new structure into `Buffer` after `ALTER` query. Fixes [#15117](https://github.com/ClickHouse/ClickHouse/issues/15117). [#15192](https://github.com/ClickHouse/ClickHouse/pull/15192) ([alesapin](https://github.com/alesapin)).
* Backported in [#15405](https://github.com/ClickHouse/ClickHouse/issues/15405): Fix instance crash when using joinGet with LowCardinality types. This fixes [#15214](https://github.com/ClickHouse/ClickHouse/issues/15214). [#15220](https://github.com/ClickHouse/ClickHouse/pull/15220) ([Amos Bird](https://github.com/amosbird)).
* Backported in [#15489](https://github.com/ClickHouse/ClickHouse/issues/15489): Fix 'Unknown identifier' in GROUP BY when query has JOIN over Merge table. [#15242](https://github.com/ClickHouse/ClickHouse/pull/15242) ([Artem Zuikov](https://github.com/4ertus2)).
* Backported in [#15281](https://github.com/ClickHouse/ClickHouse/issues/15281): Fix MSan report in QueryLog. Uninitialized memory can be used for the field `memory_usage`. [#15258](https://github.com/ClickHouse/ClickHouse/pull/15258) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
* Backported in [#15402](https://github.com/ClickHouse/ClickHouse/issues/15402): Fix hang of queries with a lot of subqueries to same table of `MySQL` engine. Previously, if there were more than 16 subqueries to same `MySQL` table in query, it hang forever. [#15299](https://github.com/ClickHouse/ClickHouse/pull/15299) ([Anton Popov](https://github.com/CurtizJ)).
* Backported in [#15338](https://github.com/ClickHouse/ClickHouse/issues/15338): Fix rare race condition on server startup when system.logs are enabled. [#15300](https://github.com/ClickHouse/ClickHouse/pull/15300) ([alesapin](https://github.com/alesapin)).
* Backported in [#15334](https://github.com/ClickHouse/ClickHouse/issues/15334): Fix race condition during MergeTree table rename and background cleanup. [#15304](https://github.com/ClickHouse/ClickHouse/pull/15304) ([alesapin](https://github.com/alesapin)).
* Backported in [#15447](https://github.com/ClickHouse/ClickHouse/issues/15447): Report proper error when the second argument of `boundingRatio` aggregate function has a wrong type. [#15407](https://github.com/ClickHouse/ClickHouse/pull/15407) ([detailyang](https://github.com/detailyang)).
* Backported in [#15505](https://github.com/ClickHouse/ClickHouse/issues/15505): Fix bug with event subscription in DDLWorker which rarely may lead to query hangs in `ON CLUSTER`. Introduced in [#13450](https://github.com/ClickHouse/ClickHouse/issues/13450). [#15477](https://github.com/ClickHouse/ClickHouse/pull/15477) ([alesapin](https://github.com/alesapin)).
* Backported in [#15550](https://github.com/ClickHouse/ClickHouse/issues/15550): Fix `Missing columns` errors when selecting columns which absent in data, but depend on other columns which also absent in data. Fixes [#15530](https://github.com/ClickHouse/ClickHouse/issues/15530). [#15532](https://github.com/ClickHouse/ClickHouse/pull/15532) ([alesapin](https://github.com/alesapin)).
* Backported in [#15558](https://github.com/ClickHouse/ClickHouse/issues/15558): Fix bug when `ILIKE` operator stops being case insensitive if `LIKE` with the same pattern was executed. [#15536](https://github.com/ClickHouse/ClickHouse/pull/15536) ([alesapin](https://github.com/alesapin)).
* Backported in [#15726](https://github.com/ClickHouse/ClickHouse/issues/15726): Mutation might hang waiting for some non-existent part after `MOVE` or `REPLACE PARTITION` or, in rare cases, after `DETACH` or `DROP PARTITION`. It's fixed. [#15537](https://github.com/ClickHouse/ClickHouse/pull/15537) ([Alexander Tokmakov](https://github.com/tavplubix)).
* Backported in [#15652](https://github.com/ClickHouse/ClickHouse/issues/15652): Fix 'Database <db> doesn't exist.' in queries with IN and Distributed table when there's no database on initiator. [#15538](https://github.com/ClickHouse/ClickHouse/pull/15538) ([Artem Zuikov](https://github.com/4ertus2)).
* Backported in [#15629](https://github.com/ClickHouse/ClickHouse/issues/15629): Significantly reduce memory usage in AggregatingInOrderTransform/optimize_aggregation_in_order. [#15543](https://github.com/ClickHouse/ClickHouse/pull/15543) ([Azat Khuzhin](https://github.com/azat)).
* Backported in [#15585](https://github.com/ClickHouse/ClickHouse/issues/15585): Prevent the possibility of error message `Could not calculate available disk space (statvfs), errno: 4, strerror: Interrupted system call`. This fixes [#15541](https://github.com/ClickHouse/ClickHouse/issues/15541). [#15557](https://github.com/ClickHouse/ClickHouse/pull/15557) ([Alexey Milovidov](https://github.com/alexey-milovidov)).
* Backported in [#15666](https://github.com/ClickHouse/ClickHouse/issues/15666): Fixed `Element ... is not a constant expression` error when using `JSON*` function result in `VALUES`, `LIMIT` or right side of `IN` operator. [#15589](https://github.com/ClickHouse/ClickHouse/pull/15589) ([Alexander Tokmakov](https://github.com/tavplubix)).
* Backported in [#15715](https://github.com/ClickHouse/ClickHouse/issues/15715): Fix the order of destruction for resources in `ReadFromStorage` step of query plan. It might cause crashes in rare cases. Possibly connected with [#15610](https://github.com/ClickHouse/ClickHouse/issues/15610). [#15645](https://github.com/ClickHouse/ClickHouse/pull/15645) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
