### ClickHouse release v21.4.6.55-stable FIXME as compared to v21.4.5.46-stable

#### Improvement
* Backported in [#23679](https://github.com/ClickHouse/ClickHouse/issues/23679): Fixed `quantile(s)TDigest`. Added special handling of singleton centroids according to tdunning/t-digest 3.2+. Also a bug with over-compression of centroids in implementation of earlier version of the algorithm was fixed. [#23314](https://github.com/ClickHouse/ClickHouse/pull/23314) ([Vladimir Chebotarev](https://github.com/excitoon)).

#### Bug Fix
* Backported in [#23580](https://github.com/ClickHouse/ClickHouse/issues/23580): Fixed very rare race condition on background cleanup of old blocks. It might cause a block not to be deduplicated if it's too close to the end of deduplication window. [#23301](https://github.com/ClickHouse/ClickHouse/pull/23301) ([Alexander Tokmakov](https://github.com/tavplubix)).
* Backported in [#23676](https://github.com/ClickHouse/ClickHouse/issues/23676): Don't relax NOT conditions during partition pruning. This fixes [#23305](https://github.com/ClickHouse/ClickHouse/issues/23305) and [#21539](https://github.com/ClickHouse/ClickHouse/issues/21539). [#23310](https://github.com/ClickHouse/ClickHouse/pull/23310) ([Amos Bird](https://github.com/amosbird)).
* Backported in [#23583](https://github.com/ClickHouse/ClickHouse/issues/23583): * Fix bug in dict join with join_algorithm = 'auto'. Close [#23002](https://github.com/ClickHouse/ClickHouse/issues/23002). [#23312](https://github.com/ClickHouse/ClickHouse/pull/23312) ([Vladimir C](https://github.com/vdimir)).
* Backported in [#23641](https://github.com/ClickHouse/ClickHouse/issues/23641): Fix incompatible constant expression generation during partition pruning based on virtual columns. This fixes https://github.com/ClickHouse/ClickHouse/pull/21401#discussion_r611888913. [#23366](https://github.com/ClickHouse/ClickHouse/pull/23366) ([Amos Bird](https://github.com/amosbird)).
* Backported in [#23586](https://github.com/ClickHouse/ClickHouse/issues/23586): Allow to move more conditions to `PREWHERE` as it was before version 21.1. Insufficient number of moved condtions could lead to worse performance. [#23397](https://github.com/ClickHouse/ClickHouse/pull/23397) ([Anton Popov](https://github.com/CurtizJ)).
* Backported in [#23588](https://github.com/ClickHouse/ClickHouse/issues/23588): Fixed `Cannot unlink file` error on unsuccessful creation of ReplicatedMergeTree table with multidisk configuration. This closes [#21755](https://github.com/ClickHouse/ClickHouse/issues/21755). [#23433](https://github.com/ClickHouse/ClickHouse/pull/23433) ([Alexander Tokmakov](https://github.com/tavplubix)).
* Backported in [#23591](https://github.com/ClickHouse/ClickHouse/issues/23591): Fix corner cases in vertical merges with `ReplacingMergeTree`. In rare cases they could lead to fails of merges with exceptions like `Incomplete granules are not allowed while blocks are granules size`. [#23459](https://github.com/ClickHouse/ClickHouse/pull/23459) ([Anton Popov](https://github.com/CurtizJ)).
* Backported in [#23611](https://github.com/ClickHouse/ClickHouse/issues/23611): Fix restart / stop command hanging. Closes [#20214](https://github.com/ClickHouse/ClickHouse/issues/20214). [#23552](https://github.com/ClickHouse/ClickHouse/pull/23552) ([filimonov](https://github.com/filimonov)).
* Backported in [#23693](https://github.com/ClickHouse/ClickHouse/issues/23693): Fixed server fault when inserting data through HTTP caused an exception. This fixes [#23512](https://github.com/ClickHouse/ClickHouse/issues/23512). [#23643](https://github.com/ClickHouse/ClickHouse/pull/23643) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Backported in [#23695](https://github.com/ClickHouse/ClickHouse/issues/23695): Added an exception in case of completely the same values in both samples in aggregate function `mannWhitneyUTest`. This fixes [#23646](https://github.com/ClickHouse/ClickHouse/issues/23646). [#23654](https://github.com/ClickHouse/ClickHouse/pull/23654) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Backported in [#23774](https://github.com/ClickHouse/ClickHouse/issues/23774): Avoid possible "Cannot schedule a task" error (in case some exception had been occurred) on INSERT into Distributed. [#23744](https://github.com/ClickHouse/ClickHouse/pull/23744) ([Azat Khuzhin](https://github.com/azat)).