2020 Changelog

[Edit this page](https://github.com/ClickHouse/clickhouse-docs/blob/main/docs/whats-new/changelog/2020.md)

### ClickHouse release 20.12[​](#clickhouse-release-2012 "Direct link to ClickHouse release 20.12")

### ClickHouse release v20.12.5.14-stable, 2020-12-28[​](#clickhouse-release-v2012514-stable-2020-12-28 "Direct link to ClickHouse release v20.12.5.14-stable, 2020-12-28")

#### Bug Fix[​](#bug-fix "Direct link to Bug Fix")

- Disable write with AIO during merges because it can lead to extremely rare data corruption of primary key columns during merge. [#18481](https://github.com/ClickHouse/ClickHouse/pull/18481) ([alesapin](https://github.com/alesapin)).
- Fixed `value is too short` error when executing `toType(...)` functions (`toDate`, `toUInt32`, etc) with argument of type `Nullable(String)`. Now such functions return `NULL` on parsing errors instead of throwing exception. Fixes [#7673](https://github.com/ClickHouse/ClickHouse/issues/7673). [#18445](https://github.com/ClickHouse/ClickHouse/pull/18445) ([tavplubix](https://github.com/tavplubix)).
- Restrict merges from wide to compact parts. In case of vertical merge it led to broken result part. [#18381](https://github.com/ClickHouse/ClickHouse/pull/18381) ([Anton Popov](https://github.com/CurtizJ)).
- Fix filling table `system.settings_profile_elements`. This PR fixes [#18231](https://github.com/ClickHouse/ClickHouse/issues/18231). [#18379](https://github.com/ClickHouse/ClickHouse/pull/18379) ([Vitaly Baranov](https://github.com/vitlibar)).
- Fix possible crashes in aggregate functions with combinator `Distinct`, while using two-level aggregation. Fixes [#17682](https://github.com/ClickHouse/ClickHouse/issues/17682). [#18365](https://github.com/ClickHouse/ClickHouse/pull/18365) ([Anton Popov](https://github.com/CurtizJ)).
- Fix error when query `MODIFY COLUMN ... REMOVE TTL` does not actually remove column TTL. [#18130](https://github.com/ClickHouse/ClickHouse/pull/18130) ([alesapin](https://github.com/alesapin)).

#### Build/Testing/Packaging Improvement[​](#buildtestingpackaging-improvement "Direct link to Build/Testing/Packaging Improvement")

- Update timezones info to 2020e. [#18531](https://github.com/ClickHouse/ClickHouse/pull/18531) ([alesapin](https://github.com/alesapin)).

### ClickHouse release v20.12.4.5-stable, 2020-12-24[​](#clickhouse-release-v201245-stable-2020-12-24 "Direct link to ClickHouse release v20.12.4.5-stable, 2020-12-24")

#### Bug Fix[​](#bug-fix-1 "Direct link to Bug Fix")

- Fixed issue when `clickhouse-odbc-bridge` process is unreachable by server on machines with dual IPv4/IPv6 stack; - Fixed issue when ODBC dictionary updates are performed using malformed queries and/or cause crashes; Possibly closes [#14489](https://github.com/ClickHouse/ClickHouse/issues/14489). [#18278](https://github.com/ClickHouse/ClickHouse/pull/18278) ([Denis Glazachev](https://github.com/traceon)).
- Fixed key comparison between Enum and Int types. This fixes [#17989](https://github.com/ClickHouse/ClickHouse/issues/17989). [#18214](https://github.com/ClickHouse/ClickHouse/pull/18214) ([Amos Bird](https://github.com/amosbird)).
- Fixed unique key convert crash in `MaterializeMySQL` database engine. This fixes [#18186](https://github.com/ClickHouse/ClickHouse/issues/18186) and fixes [#16372](https://github.com/ClickHouse/ClickHouse/issues/16372) [#18211](https://github.com/ClickHouse/ClickHouse/pull/18211) ([Winter Zhang](https://github.com/zhang2014)).
- Fixed `std::out_of_range: basic_string` in S3 URL parsing. [#18059](https://github.com/ClickHouse/ClickHouse/pull/18059) ([Vladimir Chebotarev](https://github.com/excitoon)).
- Fixed the issue when some tables not synchronized to ClickHouse from MySQL caused by the fact that convertion MySQL prefix index wasn't supported for MaterializeMySQL. This fixes [#15187](https://github.com/ClickHouse/ClickHouse/issues/15187) and fixes [#17912](https://github.com/ClickHouse/ClickHouse/issues/17912) [#17944](https://github.com/ClickHouse/ClickHouse/pull/17944) ([Winter Zhang](https://github.com/zhang2014)).
- Fixed the issue when query optimization was producing wrong result if query contains `ARRAY JOIN`. [#17887](https://github.com/ClickHouse/ClickHouse/pull/17887) ([sundyli](https://github.com/sundy-li)).
- Fixed possible segfault in `topK` aggregate function. This closes [#17404](https://github.com/ClickHouse/ClickHouse/issues/17404). [#17845](https://github.com/ClickHouse/ClickHouse/pull/17845) ([Maksim Kita](https://github.com/kitaisreal)).
- Fixed empty `system.stack_trace` table when server is running in daemon mode. [#17630](https://github.com/ClickHouse/ClickHouse/pull/17630) ([Amos Bird](https://github.com/amosbird)).

### ClickHouse release v20.12.3.3-stable, 2020-12-13[​](#clickhouse-release-v201233-stable-2020-12-13 "Direct link to ClickHouse release v20.12.3.3-stable, 2020-12-13")

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

- Enable `use_compact_format_in_distributed_parts_names` by default (see the documentation for the reference). [#16728](https://github.com/ClickHouse/ClickHouse/pull/16728) ([Azat Khuzhin](https://github.com/azat)).
- Accept user settings related to file formats (e.g. `format_csv_delimiter`) in the `SETTINGS` clause when creating a table that uses `File` engine, and use these settings in all `INSERT`s and `SELECT`s. The file format settings changed in the current user session, or in the `SETTINGS` clause of a DML query itself, no longer affect the query. [#16591](https://github.com/ClickHouse/ClickHouse/pull/16591) ([Alexander Kuzmenkov](https://github.com/akuzm)).

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