2021 Changelog

### ClickHouse release v21.10, 2021-10-16. [Presentation](https://presentations.clickhouse.com/2021-release-21.10/), [Video](https://www.youtube.com/watch?v=b9MeoOtAivQ)[​](#clickhouse-release-v2110-2021-10-16 "Direct link to clickhouse-release-v2110-2021-10-16")

#### Backward Incompatible Change[​](#backward-incompatible-change-2 "Direct link to Backward Incompatible Change")

- Now the following MergeTree table-level settings: `replicated_max_parallel_sends`, `replicated_max_parallel_sends_for_table`, `replicated_max_parallel_fetches`, `replicated_max_parallel_fetches_for_table` do nothing. They never worked well and were replaced with `max_replicated_fetches_network_bandwidth`, `max_replicated_sends_network_bandwidth` and `background_fetches_pool_size`. [#28404](https://github.com/ClickHouse/ClickHouse/pull/28404) ([alesapin](https://github.com/alesapin)).

#### New Feature[​](#new-feature-2 "Direct link to New Feature")

- Add feature for creating user-defined functions (UDF) as lambda expressions. Syntax `CREATE FUNCTION {function_name} as ({parameters}) -> {function core}`. Example `CREATE FUNCTION plus_one as (a) -> a + 1`. Authors @Realist007. [#27796](https://github.com/ClickHouse/ClickHouse/pull/27796) ([Maksim Kita](https://github.com/kitaisreal)) [#23978](https://github.com/ClickHouse/ClickHouse/pull/23978) ([Realist007](https://github.com/Realist007)).
- Added `Executable` storage engine and `executable` table function. It enables data processing with external scripts in streaming fashion. [#28102](https://github.com/ClickHouse/ClickHouse/pull/28102) ([Maksim Kita](https://github.com/kitaisreal)) ([ruct](https://github.com/ruct)).
- Added `ExecutablePool` storage engine. Similar to `Executable` but it's using a pool of long running processes. [#28518](https://github.com/ClickHouse/ClickHouse/pull/28518) ([Maksim Kita](https://github.com/kitaisreal)).
- Add `ALTER TABLE ... MATERIALIZE COLUMN` query. [#27038](https://github.com/ClickHouse/ClickHouse/pull/27038) ([Vladimir Chebotarev](https://github.com/excitoon)).
- Support for partitioned write into `s3` table function. [#23051](https://github.com/ClickHouse/ClickHouse/pull/23051) ([Vladimir Chebotarev](https://github.com/excitoon)).
- Support `lz4` compression format (in addition to `gz`, `bz2`, `xz`, `zstd`) for data import / export. [#25310](https://github.com/ClickHouse/ClickHouse/pull/25310) ([Bharat Nallan](https://github.com/bharatnc)).
- Allow positional arguments under setting `enable_positional_arguments`. Closes [#2592](https://github.com/ClickHouse/ClickHouse/issues/2592). [#27530](https://github.com/ClickHouse/ClickHouse/pull/27530) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Accept user settings related to file formats in `SETTINGS` clause in `CREATE` query for s3 tables. This closes [#27580](https://github.com/ClickHouse/ClickHouse/issues/27580). [#28037](https://github.com/ClickHouse/ClickHouse/pull/28037) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
- Allow SSL connection for `RabbitMQ` engine. [#28365](https://github.com/ClickHouse/ClickHouse/pull/28365) ([Kseniia Sumarokova](https://github.com/kssenii)).
- Add `getServerPort` function to allow getting server port. When the port is not used by the server, throw an exception. [#27900](https://github.com/ClickHouse/ClickHouse/pull/27900) ([Amos Bird](https://github.com/amosbird)).
- Add conversion functions between "snowflake id" and `DateTime`, `DateTime64`. See [#27058](https://github.com/ClickHouse/ClickHouse/issues/27058). [#27704](https://github.com/ClickHouse/ClickHouse/pull/27704) ([jasine](https://github.com/jasine)).
- Add function `SHA512`. [#27830](https://github.com/ClickHouse/ClickHouse/pull/27830) ([zhanglistar](https://github.com/zhanglistar)).
- Add `log_queries_probability` setting that allows user to write to query\_log only a sample of queries. Closes [#16609](https://github.com/ClickHouse/ClickHouse/issues/16609). [#27527](https://github.com/ClickHouse/ClickHouse/pull/27527) ([Nikolay Degterinsky](https://github.com/evillique)).

#### Experimental Feature[​](#experimental-feature-2 "Direct link to Experimental Feature")

- `web` type of disks to store readonly tables on web server in form of static files. See [#23982](https://github.com/ClickHouse/ClickHouse/issues/23982). [#25251](https://github.com/ClickHouse/ClickHouse/pull/25251) ([Kseniia Sumarokova](https://github.com/kssenii)). This is mostly needed to faciliate testing of operation on shared storage and for easy importing of datasets. Not recommended to use before release 21.11.
- Added new commands `BACKUP` and `RESTORE`. [#21945](https://github.com/ClickHouse/ClickHouse/pull/21945) ([Vitaly Baranov](https://github.com/vitlibar)). This is under development and not intended to be used in current version.

#### Performance Improvement[​](#performance-improvement-2 "Direct link to Performance Improvement")

- Speed up `sumIf` and `countIf` aggregation functions. [#28272](https://github.com/ClickHouse/ClickHouse/pull/28272) ([Raúl Marín](https://github.com/Algunenano)).
- Create virtual projection for `minmax` indices. Now, when `allow_experimental_projection_optimization` is enabled, queries will use minmax index instead of reading the data when possible. [#26286](https://github.com/ClickHouse/ClickHouse/pull/26286) ([Amos Bird](https://github.com/amosbird)).
- Introducing two checks in `sequenceMatch` and `sequenceCount` that allow for early exit when some deterministic part of the sequence pattern is missing from the events list. This change unlocks many queries that would previously fail due to reaching operations cap, and generally speeds up the pipeline. [#27729](https://github.com/ClickHouse/ClickHouse/pull/27729) ([Jakub Kuklis](https://github.com/jkuklis)).
- Enhance primary key analysis with always monotonic information of binary functions, notably non-zero constant division. [#28302](https://github.com/ClickHouse/ClickHouse/pull/28302) ([Amos Bird](https://github.com/amosbird)).
- Make `hasAll` filter condition leverage bloom filter data-skipping indexes. [#27984](https://github.com/ClickHouse/ClickHouse/pull/27984) ([Braulio Valdivielso Martínez](https://github.com/BraulioVM)).
- Speed up data parts loading by delaying table startup process. [#28313](https://github.com/ClickHouse/ClickHouse/pull/28313) ([Amos Bird](https://github.com/amosbird)).
- Fixed possible excessive number of conditions moved from `WHERE` to `PREWHERE` (optimization controlled by settings `optimize_move_to_prewhere`). [#28139](https://github.com/ClickHouse/ClickHouse/pull/28139) ([lthaooo](https://github.com/lthaooo)).
- Enable `optimize_distributed_group_by_sharding_key` by default. [#28105](https://github.com/ClickHouse/ClickHouse/pull/28105) ([Azat Khuzhin](https://github.com/azat)).

#### Improvement[​](#improvement-2 "Direct link to Improvement")